I recently got Fallout 3 GoTY edition and I had a similar problem with freezing. The game would freeze every 15 minutes or so but I managed to find the solution. Now a few days later instead of freezing it just gives me an error message every 15 minutes and closes the program. I don't think its a problem with my graphics or anything because theres very very little lag and the game sets my settings to high. Does anyone have a solution?

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.

Also, what is the error that is being displayed?