crashes all the time

I have Edubuntu 6.06 LTS on a x64 architechture. It randomly crashes
while with FF, OOo, and just now with Abiword. I just lost a huge chunk
(10 pages) of editing that my girlfriend was doing for me for an
important research paper- she is positively keeping Vista on her Windows
laptop now - I just lost that argument. She was saving all the time onto
a USB stick to prevent this from happening. It did

This has been happening since I first installed Ubuntu 7.04 so then I
switched down to the LTS - and as I am I teacher I went to Edubuntu.

The screen goes (all white with a few vertical lines that
are different every time) and the machine becomes absolutely unusable -
I have to reset it.

Xubuntu 7.04 on my crappy old laptop has never done this.

this seems less a bug than an near unusable OS for my hardware.

what can I do? is it a hardware thing? I built the machine myself - I
had lots of difficulty trying to find a list stating which motherboard
etc. Ubuntu x64 would was all compatible with.