This happens sometimes when you force anti aliasing from the Nvidia control panel, instead of letting the application decide.
I am using a... NVIDIA GeForce 7800 GS and my OS is XP.
I use a 6800 GS and use Xp as well
I played around in-game with this months ago, if you turn off green-tint, the problem is solved. Doesnt matter what setting you have in-game as long as you have green-tint off this wont happen.
P.S. Turn off overbright for better performance less lag.