I just got Fallout 3 today and instantly had a problem with the game as soon as I exited the vault. Basically when I look around in-game will lag for half a second once or multiple times. I lowered my settings from ultra high to high and still same problem. I then lowered the settings lower and still the same problem. I went to go edit my nHancer settings and nHancer cannot even find Fallout 3 on my computer. Not sure what the problem is there.

My specs:

Q6600 @ 2.4GHz
3GB RAM
GTS 250 1GB (drivers 197.45)
Windows 7 64-bit

Well, took me an hour but I figured it out and fixed the problem. Just simple downgraded to driver 188.25.