Bootcamped Windows of course.
But I'm afraid your MacBook won't run any new games due to incredibly crappy Intel video chip
The intel x3100 is a garbage video card. You can play sims 1 with it. I play a lot of FPS, the only one that works decently with my macbook is counter-strike (the original).
I get around 30fps in WoW. If I am lucky, and all of the settings are on low. On my Quad-core (2.4), 4 Gigs of Ram, and a nvidia 8800gt 512 MB DDR3, I get 60 fps easy. I bring this up because my macbook and my desktop have the same clock speed processors (4 cores doesnt do much for games), same amount of ram, and the only real difference is the piece of crap video card, and a high end video card. The resolution on my desktop is 1600 by 900, laptop 1200 by 800.
I have to have a special windows only pc to play games because my games will not play. I can play d00m 3 on high on my desktop 60FPS.
I am playing older games, and the performance is bad.