Fallout 3 had a lot of problems but I run the Steam version on Windows 7 x64 and Linux and it generally only crashes every two or three hours.
One specific fix I applied was required to run reliably on a quad-core CPU; there's a configuration file where you need to change a couple of lines to avoid random crashes soon after starting or loading a game. If you're running on a quad-core then the Steam forum has the details if you can't find it anywhere else.