.....but CoD4 runs fine. The FPS stays above 40 ALMOST all the time, the lowest I've seen it is 30, but the GAME still feels unresponsive and jerky. I've tried lowering the settings but that only increased the FPS and the game was still stuttering. No problems with any other games. I've tried defragging and setting the affinity for the game to only ONE core in task manager (it fixes stuttering in some games like NFS MW). I have the latest patch. My Specs:

AMD ATHLON X2 64 2.2 GHz 4200+
1 GB RAM
XFX GeForce 8600 265 MB

That is a tough problem there. I have no idea to help.You meet the specs pretty well. What OS are you running?
Try using the lowest possible settings. Any change?
I would suggesting closing all un-needed programs (and check that using Task Manager) and then trying again.Problem seems to have gone away randomly. Thanks for the help. (running XP btw)All right. I guess it was a one time thing then.
Sometimes if you're like downloading a large file or you have many programs running in the background or LISTENING to music, they take up resources the game needs so it will lag.
That might of been your problem.