Mine does exactly the same thing!

I installed just fine, played for about 2 hours... Then I quit out. When I run it again, I get to the main menu just fine. But when I load my save game or try to start a new game, it loads for a few seconds then crashes. I get the Windows "Fallout 3 has stopped working" dialog. This sucks!!! :-(

ATI HD4850

Windows Vista Ultimate x64

Retail DVD Fallout 3

Q6600