First, please do not double post a thread.
Second...use the search function.
Third....check the posts....if you had done that before posting, than you would be able to play the game.
All you need to do is setting up the fallout.ini. Since you got a 64 Bit System, you also have a Dual or Quad Core.
So you need to tell the game, that it has to run with one (better choice) or maximum two cores.
There are more than five threads, where you can find a perfect explanation.
Since Fallout 3 is a little bit older, it has problems to run with computers with more than one Core.
Just stop being lazy and get the information yourself.