I'm got a second generation Macbook Pro w/ 4 gigs of ram, a nvidia 9400 graphics card, and a hard drive w/ 320 gb @720 RPM.
And I have Windows installed on it. Mind you, it's via boot camp. I use my Mac for everything except gaming, and I use Windows (with an 80 gb hard drive partition) for gaming ONLY. I can even play Assassin's Creed at max graphics without a hitch in gameplay.
So, PCs are best for gaming, but only because they have games. If the Mac had games, it would own the PC's ass.