You should have pretty good performance with your system. Don't expect 1600x1200 max detail but I'm sure at 1024x768 your system should have no problem running max details I think.
Me I'll stick to my 733MHz xbox and smooth Halo hehe. I think it's actually kinda fun with a controller and not a KB+mouse. Or maybe that's just because I first played Halo on the xbox and don't want to taint the game experience.
Anyways good luck and happy gaming!
Ruahrc