For those of you who can run this game at 60 fps without ANY slowdown, try changing iFPSClamp=0 to iFPSClamp=60 in the fallout.ini file (under "Documents\My Games\Fallout3\FALLOUT.ini). By default, the game has this constant jumpy feeling that ruins the fluidity of 60 fps. Try panning the camera around and you'll see what I mean. I think this actually has an impact on basically every PC. It drove me nuts until I changed that setting.
Having read up on it, however, it turns out that this was set to zero in order to maintain game speed under all framerate conditions. If you set it to 60, your framerate MUST remain 60 fps at all times else the actual game speed will drop (ie - game will run in slow motion). You'll need v-sync enabled for this to work as well. If your machine is up to it and you're using v-sync, this will result in a much smoother Fallout 3 experience. It looks fantastic. I'm just happy that I'm able to run the game with Ultra settings + AA + AF and still get 60 fps 100% of the time. Easily the most optimized Bethsoft experience I've played to date.
i think when you use VATS you are invulnerable from enemy gunfire.
That doesn't seem to be the case. I was attacked by 4 guys at once and, while using VATS (during the animation), my character was still taking damage. There were just too many bullets flying. Same deal with the fire ants (if you use VATS while you're being lit up you will still take damage).