Just a reminder - the PC version of Fallout 3 has Xbox Live Achievements, like Halo 2 (PC) and Shadowrun (PC) do. In other words, you can earn points for your Live Gamerscore and even chat with people on your friends list with Fallout 3 on your PC.
The Achievements are identical to the Xbox 360 achievements. If you're really clever like me, you buy the PC version and rent the Xbox 360 version - double Achievements. (You can't rent PC games, unfortunately.)