Ubuntu crashes frequently when I move the mouse; also sometimes when I open my browser.

Please try:
sudo apt-get upgrade

Please also post output of:
free -m
df -h
sudo lshw -C video
/usr/lib/nux/unity_support_test -p

Thanks.

OK, here is what happened when I pasted and entered sudo-get upgrade....

leokn@leokn-desktop:~$ sudo apt-get upgrade
[sudo] password for leokn:
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages will be upgraded:
  bzip2 cups cups-bsd cups-client cups-common cups-ppdc isc-dhcp-client isc-dhcp-common libbz2-1.0 libcups2
  libcups2-dev libcupscgi1 libcupsdriver1 libcupsimage2 libcupsimage2-dev libcupsmime1 libcupsppdc1
17 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Need to get 4,267 kB of archives.
After this operation, 24.6 kB disk space will be freed.
Do you want to continue [Y/n]? Y
Get:1 http://us.archive.ubuntu.com/ubuntu/ oneiric-updates/main libcupsimage2-dev i386 1.5.0-8ubuntu6 [65.1 kB]
Get:2 http://us.archive.ubuntu.com/ubuntu/ oneiric-updates/main libcupsimage2 i386 1.5.0-8ubuntu6 [54.1 kB]
Get:3 http://us.archive.ubuntu.com/ubuntu/ oneiric-updates/main libcups2-dev i386 1.5.0-8ubuntu6 [237 kB]
Get:4 http://us.archive.ubuntu.com/ubuntu/ oneiric-updates/main libcups2 i386 1.5.0-8ubuntu6 [174 kB]
Get:5 http://us.archive.ubuntu.com/ubuntu/ oneiric-updates/main libcupscgi1 i386 1.5.0-8ubuntu6 [32.7 kB]
Get:6 http://us.archive.ubuntu.com/ubuntu/ oneiric-updates/main libcupsdriver1 i386 1.5.0-8ubuntu6 [22.4 kB]
Get:7 http://us.archive.ubuntu.com/ubuntu/ oneiric-updates/main libcupsmime1 i386 1.5.0-8ubuntu6 [16.0 kB]
Get:8 http://us.archive.ubuntu.com/ubuntu/ oneiric-updates/main libcupsppdc1 i386 1.5.0-8ubuntu6 [55.4 kB]
Get:9 http://us.archive.ubuntu.com/ubuntu/ oneiric-updates/main bzip2 i386 1.0.5-6ubuntu1.11.10.1 [36.8 kB]
Get:10 http://us.archive.ubuntu.com/ubuntu/ oneiric-updates/main libbz2-1.0 i386 1.0.5-6ubuntu1.11.10.1 [33.5 kB]
Get:11 http://us.archive.ubuntu.com/ubuntu/ oneiric-updates/main isc-dhcp-client i386 4.1.1-P1-17ubuntu10.1 [286 kB]
Get:12 http://us.archive.ubuntu.com/ubuntu/ oneiric-updates/main isc-dhcp-common i386 4.1.1-P1-17ubuntu10.1 [338 kB]
Get:13 http://us.archive.ubuntu.com/ubuntu/ oneiric-updates/main cups-common all 1.5.0-8ubuntu6 [711 kB]
Get:14 http://us.archive.ubuntu.com/ubuntu/ oneiric-updates/main cups-bsd i386 1.5.0-8ubuntu6 [43.4 kB]
Get:15 http://us.archive.ubuntu.com/ubuntu/ oneiric-updates/main cups-client i386 1.5.0-8ubuntu6 [161 kB]
Get:16 http://us.archive.ubuntu.com/ubuntu/ oneiric-updates/main cups-ppdc i386 1.5.0-8ubuntu6 [31.8 kB]
Get:17 http://us.archive.ubuntu.com/ubuntu/ oneiric-updates/main cups i386 1.5.0-8ubuntu6 [1,969 kB]
Fetched 4,267 kB in 13s (309 kB/s)
Preconfiguring packages ...
(Reading database ... 195876 files and directories currently installed.)
Preparing to replace libcupsimage2-dev 1.5.0-8ubuntu5 (using .../libcupsimage2-dev_1.5.0-8ubuntu6_i386.deb) ...
Unpacking replacement libcupsimage2-dev ...
Preparing to replace libcupsimage2 1.5.0-8ubuntu5 (using .../libcupsimage2_1.5.0-8ubuntu6_i386.deb) ...
Unpacking replacement libcupsimage2 ...
Preparing to replace libcups2-dev 1.5.0-8ubuntu5 (using .../libcups2-dev_1.5.0-8ubuntu6_i386.deb) ...
Unpacking replacement libcups2-dev ...
Preparing to replace libcups2 1.5.0-8ubuntu5 (using .../libcups2_1.5.0-8ubuntu6_i386.deb) ...
Unpacking replacement libcups2 ...
Preparing to replace libcupscgi1 1.5.0-8ubuntu5 (using .../libcupscgi1_1.5.0-8ubuntu6_i386.deb) ...
Unpacking replacement libcupscgi1 ...
Preparing to replace libcupsdriver1 1.5.0-8ubuntu5 (using .../libcupsdriver1_1.5.0-8ubuntu6_i386.deb) ...
Unpacking replacement libcupsdriver1 ...
Preparing to replace libcupsmime1 1.5.0-8ubuntu5 (using .../libcupsmime1_1.5.0-8ubuntu6_i386.deb) ...
Unpacking replacement libcupsmime1 ...
Preparing to replace libcupsppdc1 1.5.0-8ubuntu5 (using .../libcupsppdc1_1.5.0-8ubuntu6_i386.deb) ...
Unpacking replacement libcupsppdc1 ...
Preparing to replace bzip2 1.0.5-6ubuntu1 (using .../bzip2_1.0.5-6ubuntu1.11.10.1_i386.deb) ...
Unpacking replacement bzip2 ...
Preparing to replace libbz2-1.0 1.0.5-6ubuntu1 (using .../libbz2-1.0_1.0.5-6ubuntu1.11.10.1_i386.deb) ...
Unpacking replacement libbz2-1.0 ...
Processing triggers for man-db ...
Setting up libbz2-1.0 (1.0.5-6ubuntu1.11.10.1) ...
Processing triggers for libc-bin ...
ldconfig deferred processing now taking place
(Reading database ... 195876 files and directories currently installed.)
Preparing to replace isc-dhcp-client 4.1.1-P1-17ubuntu10 (using .../isc-dhcp-client_4.1.1-P1-17ubuntu10.1_i386.deb) ...
Unpacking replacement isc-dhcp-client ...
Preparing to replace isc-dhcp-common 4.1.1-P1-17ubuntu10 (using .../isc-dhcp-common_4.1.1-P1-17ubuntu10.1_i386.deb) ...
Unpacking replacement isc-dhcp-common ...
Preparing to replace cups-common 1.5.0-8ubuntu5 (using .../cups-common_1.5.0-8ubuntu6_all.deb) ...
Unpacking replacement cups-common ...
Preparing to replace cups-bsd 1.5.0-8ubuntu5 (using .../cups-bsd_1.5.0-8ubuntu6_i386.deb) ...
Unpacking replacement cups-bsd ...
Preparing to replace cups-client 1.5.0-8ubuntu5 (using .../cups-client_1.5.0-8ubuntu6_i386.deb) ...
Unpacking replacement cups-client ...
Preparing to replace cups-ppdc 1.5.0-8ubuntu5 (using .../cups-ppdc_1.5.0-8ubuntu6_i386.deb) ...
Unpacking replacement cups-ppdc ...
Preparing to replace cups 1.5.0-8ubuntu5 (using .../cups_1.5.0-8ubuntu6_i386.deb) ...
cups stop/waiting
Unpacking replacement cups ...
Processing triggers for man-db ...
Processing triggers for ureadahead ...
ureadahead will be reprofiled on next reboot
Processing triggers for ufw ...
Processing triggers for doc-base ...
Processing 1 changed doc-base file...
Registering documents with scrollkeeper...
Setting up libcups2 (1.5.0-8ubuntu6) ...
Setting up libcupsimage2 (1.5.0-8ubuntu6) ...
Setting up libcups2-dev (1.5.0-8ubuntu6) ...
Setting up libcupsimage2-dev (1.5.0-8ubuntu6) ...
Setting up libcupscgi1 (1.5.0-8ubuntu6) ...
Setting up libcupsdriver1 (1.5.0-8ubuntu6) ...
Setting up libcupsmime1 (1.5.0-8ubuntu6) ...
Setting up libcupsppdc1 (1.5.0-8ubuntu6) ...
Setting up bzip2 (1.0.5-6ubuntu1.11.10.1) ...
Setting up isc-dhcp-common (4.1.1-P1-17ubuntu10.1) ...
Setting up isc-dhcp-client (4.1.1-P1-17ubuntu10.1) ...
Setting up cups-common (1.5.0-8ubuntu6) ...
Setting up cups-client (1.5.0-8ubuntu6) ...
Setting up cups-bsd (1.5.0-8ubuntu6) ...
Setting up cups-ppdc (1.5.0-8ubuntu6) ...
Setting up cups (1.5.0-8ubuntu6) ...
cups start/running, process 4221
Updating PPD files for cups ...
Processing triggers for libc-bin ...
ldconfig deferred processing now taking place
leokn@leokn-desktop:~$
leokn@leokn-desktop:~$

.....the reason for the last 2 lines repeating is the cursor was not blinking, so I hit <enter>, and then the line repeated, this time with a blinking cursor. By the way, when I wait a short while before moving or clicking the mouse, I get fewer crashes. I have a Pentium III with one memory stick of 256 MB PC133, and two matching sticks of 128 MB PC100.

I will now return here after getting the output of your second suggestion. Thank you for your help! ~Leo

Here is my output from your second suggestion...

leokn@leokn-desktop:~$ leokn@leokn-desktop:~$ free -m
roduct: NV6 [Vanta/Vanta LT]
       vendor: nVidia Corporation
       physical id: 0
       bus info: pci@0000:02:00.0
       version: 15
       width: 32 bits
       clock: 66MHz
       capabilities: pm agp agp-2.0 vga_controller bus_master cap_list
       configuration: latency=64 maxlatency=1 mingnt=5
       resources: memory:fd000000-fdffffff memory:f2000000-f3ffffff memory:feaf0000-feafffff
leokn@leokn-desktop:~$ /usr/lib/nux/unity_support_test -p
OpenGL vendor string: Mesa Project
OpenGL renderer string: Software Rasterizer
OpenGL version string: 2.1 Mesa 7.11

Not software rendered: no
Not blacklisted: yes
GLX fbconfig: yes
GLX texture from pixmap: no
GL npot or rect textures: yes
GL vertex program: yes
GL fragment program: yes
GL vertex buffer object: yes
GL framebuffer object: yes
GL version is 1.4+: yes

Unity 3D supported: no
leokn@leokn-desktop:~$
leokn@leokn-desktop:~$: command not found
leokn@leokn-desktop:~$ total used free shared buffers cached
The program 'total' is currently not installed. You can install it by typing:
sudo apt-get install radiance
leokn@leokn-desktop:~$ Mem: 496 359 136 0 10 124
Mem:: command not found
leokn@leokn-desktop:~$ -/+ buffers/cache: 224 271
bash: -/+: No such file or directory
leokn@leokn-desktop:~$ Swap: 509 39 470
Swap:: command not found
leokn@leokn-desktop:~$ leokn@leokn-desktop:~$ df -h
leokn@leokn-desktop:~$: command not found
leokn@leokn-desktop:~$ Filesystem Size Used Avail Use% Mounted on
Filesystem: command not found
leokn@leokn-desktop:~$ /dev/sdb1 37G 16G 19G 45% /
bash: /dev/sdb1: Permission denied
leokn@leokn-desktop:~$ udev 242M 4.0K 242M 1% /dev
No command 'udev' found, did you mean:
 Command 'udv' from package 'ncbi-tools-x11' (universe)
 Command 'udav' from package 'udav' (universe)
 Command 'udevd' from package 'udev' (main)
udev: command not found
leokn@leokn-desktop:~$ tmpfs 100M 744K 99M 1% /run
No command 'tmpfs' found, did you mean:
 Command 'mtpfs' from package 'mtpfs' (universe)
tmpfs: command not found
leokn@leokn-desktop:~$ none 5.0M 0 5.0M 0% /run/lock
No command 'none' found, did you mean:
 Command 'nona' from package 'hugin-tools' (universe)
 Command 'one' from package 'opennebula' (universe)
 Command 'note' from package 'note' (universe)
 Command 'cone' from package 'cone' (universe)
 Command 'node' from package 'node' (universe)
 Command 'node' from package 'nodejs' (universe)
none: command not found
leokn@leokn-desktop:~$ none 249M 176K 248M 1% /run/shm
No command 'none' found, did you mean:
 Command 'nona' from package 'hugin-tools' (universe)
 Command 'one' from package 'opennebula' (universe)
 Command 'note' from package 'note' (universe)
 Command 'cone' from package 'cone' (universe)
 Command 'node' from package 'node' (universe)
 Command 'node' from package 'nodejs' (universe)
none: command not found
leokn@leokn-desktop:~$ leokn@leokn-desktop:~$ sudo lshw -C video
leokn@leokn-desktop:~$: command not found
leokn@leokn-desktop:~$ [sudo] password for leokn:
[sudo]: command not found
leokn@leokn-desktop:~$ Sorry, try again.
Sorry,: command not found
leokn@leokn-desktop:~$ [sudo] password for leokn:
[sudo]: command not found
leokn@leokn-desktop:~$ PCI (sysfs)
bash: syntax error near unexpected token `sysfs'
leokn@leokn-desktop:~$ free -m
             total used free shared buffers cached
Mem: 496 370 126 0 12 132
-/+ buffers/cache: 225 271
Swap: 509 39 470
leokn@leokn-desktop:~$ df -h
Filesystem Size Used Avail Use% Mounted on
/dev/sdb1 37G 16G 19G 45% /
udev 242M 4.0K 242M 1% /dev
tmpfs 100M 744K 99M 1% /run
none 5.0M 0 5.0M 0% /run/lock
none 249M 176K 248M 1% /run/shm
leokn@leokn-desktop:~$ sudo lshw -C video
[sudo] password for leokn:
Sorry, try again.
[sudo] password for leokn:
  *-display UNCLAIMED
       description: VGA compatible controller
       product: NV6 [Vanta/Vanta LT]
       vendor: nVidia Corporation
       physical id: 0
       bus info: pci@0000:02:00.0
       version: 15
       width: 32 bits
       clock: 66MHz
       capabilities: pm agp agp-2.0 vga_controller bus_master cap_list
       configuration: latency=64 maxlatency=1 mingnt=5
       resources: memory:fd000000-fdffffff memory:f2000000-f3ffffff memory:feaf0000-feafffff
leokn@leokn-desktop:~$

Thanks, appreciate the ouputs, since one can visualize the uncomfortable experience.
Upgrade output looks fine, but graphic and RAM look rather less supported.
You need at least 1 GB RAM and a proper graphic card with enabled 3d support to run Unity-3d.
https://wiki.ubuntu.com/DemystifyingUnityGraphicsHardwareRequirements

You could try to login to Unity-2d, try Ubuntu derivatives, e.g. Xubuntu, Lubuntu
https://wiki.ubuntu.com/DerivativeTeam/Derivatives
or read about minimal installation.
https://help.ubuntu.com/community/Installation

I don't know what is meant by Unity-3d or 2d, but I did a reinstall by allowing Ubuntu to automate the change from Ubuntu to Lubuntu.

Now I can't print anything, and the system still crashes, even more so now.

Thanks Sam_, that solved my question.

I am thankful for your assistance, Sam! I installed Lubuntu 11.10 and it solved the above mentioned problems. YAY!!!
Printer works fine; no mouse crashes.
This "Frankenstein' computer I put together with spare parts...a Pent III, 512 MB mem (2 sticks of PC100 and one PC133) runs MUCH cleaner and faster than my previous P4 computer w/Windows XP. Double hooray!!!
I'll start a new thread if I can't find out what I need to do to get AdobeFlash to download (the download link takes me to my browser home page instead of the link). And....maybe I can use some other program altogether (eg, "Lightspark"?).
~Leo

Glad to see you happy. Adobe-Flash is available in repositories. Search the package manager (Synaptic, software-center) or whatever Lubuntu offers, for flash and install.
https://wiki.ubuntu.com/Lubuntu