Fallout 3 running extremely slow?

So, I just installed Fallout 3 again after getting Windows 7 over my rotten, year-old Vista install. But, for some reason it seems to run extremely slow, even on the lowest settings, dropping to under 20FPS at times. If I up to high settings, which played just fine under Vista, it barely ever goes above 20FPS, and even the mouse movement seems to lag behind. I've got the latest drivers for my GTX260, and I don't think my CPU (3.8GHz C2D) should be bottlenecking, as Fallout3.exe spikes at about 40% CPU utilization.

Any ideas?

I have had problems with the new drivers and FO3. try using 185ish drivers and i bet the problem will go away and check for game updates if you just reinstalled it.

Make sure you have it fully patched too.

Edit: gottcha, good to see another Wisconsinite on here

I am not sure where it is but in the Steam folder is an option to run under Win xp compatibility mode. Or just right click the exe and do it it there.

This fixed some problems for some , I needed to do the fix for Quad cores where you disable 2 of the cores and then I also run it Windowed as an additional insurance.

Open up the fallout.ini file in: My Documents\My Games\Fallout3
Find the line:
bUseThreadedAI=0
change it to:
bUseThreadedAI=1
Add another line after it and insert:
iNumHWThreads=2
This will limit the game to 2 cores and prevent the engine bug from causing the game to freeze.

Click to expand...

Heck of a fun game...just reached level 28 and only have a few quests and places to visit yet.

ifpsclamp=60 in your INI file I think its in my documents