The game runs fine on Windows 7. Usually the problem lies with incompatible hardware or some rogue codecs going on. And Bethesda has already stated that they are done with FO3 and have moved on to the next TES game.
Post a dxdiag.
XP: Go to Start->run, type “dxdiag” and hit enter. Click the Save All Information button near the bottom right. This will save a Dxdiag.txt in C:\ by default. Then open the dxdiag.txt and copy/paste the information into your post.
VISTA/Windows 7: Go to Start->Search, type “dxdiag” and hit enter, click the Save All Information button near the bottom right. This will save a Dxdiag.txt in C:\ by default. Then open the dxdiag.txt and copy/paste the information into your post.