how would you handle screen video in iMovie?

[deerfieldtjr]

If you are bringing it in at 640x480, it is staying at that resolution in iMovie. Recall that iMovie presents a lower resolution/quality while in the program ("preview mode") as part of resource management. When you export your completed movie out of iMovie, it will be in final, full quality which should, in your case, be as good as 640x480 can be.