Graphics card issues Macbook Pro 2.8

So I am a big Company fo Heroes fan, but still want mobility. The Macbook Pro I bought with 2.8 GHz and 512 9600M GT card played it perfect when I first bought it. I had the settings near maxed out while playing in Windows XP. Well I reinstalled windows to give myself more hd space and now the game runs jittery. Even when I put it at teh lowest settings possible it is still jittery. For example the guys walking look liek there are short pauses in every step? Does anyone know what could be the issue? I have tried switching HD's, reinstalling OS X 10.5.6, Genius bar who ran hardware diagnostics and found nothing, disabled wireless card, and tried about 5 different video drivers from laptopvideo2go.com. Does anyone have a solution or suggestion as to what they would do? I am just wondering if there is some kind of hardware issue that is not being caught. Any help at all I truely appreciate! Cam

10.5.6

I have also noticed some stuttering in Age of Empires III and Halo as well on the mac side. What would someone do or say to apple?