Imported or pasted images/graphs appear pixelated

What resolution have those bitmaps? Are they already in publication-quality?
Keep in mind that usually that if you're using an office package probably you're pasting a low resolution proxy instead of the real data.
Try to export the images from the other packages to a high resolution bitmap (300 dpi) and import them in inkscape.
I do that on daily basis and I never got pixelated images.

I cannot specify the resolution of tif files when I export them from other software packages (can you do this in Inkspace?). Copy/pasting them into PPT looks great, doing the same into Inkscape givres blurry text. What setting in Inkscape would you recommend (inches, pixels)? I believe it is just a minor setting problem, but it kills much of my time. Thanks for any responses.

You have to keep in mind that pixel size in bitmap images is a critical value. The quality of the image depends on its pixel size and if it that value is too low, it's impossible to raise the size of the image without loosing quality.
You probably don't have problems inserting the image in a PPT because it's already 72 dpi (screen resolution) and powerpoint uses that resolution for importing images, and displays it without zooming or scaling. So you are seeing the image in a 1:1 scale.
The problem is that Inkscape is a vector drawing program and you can zoom in and out, and scale up and down the resources (mostly vector curves). Bitmap images look pixelated when they are scaled up.
I think you should open the TIFF files in a program like GIMP or Photoshop and look what is their pixel size.
Then, go back to inkscape, import the image and rescale it to match the pixel size of the image, and change the zoom value to 100%
You should be able to see the image without distortion.
Anyway, if you need a 1500x1500 pixels image out of your inkscape artwork, you will need an image of that size from the program you're exporting. In that point it has nothing to do with inkscape.

Thank you very much, Guillermo.