Yeah, Jogo is pretty much spot on. I wouldn't expect much out of anything less than a recent iMac or MacBook Pro that isn't a 13". They will all play games to an extent, but not extremely well. You'll probably be able to run rFactor and Race 07, things of that vintage, adequately enough to play with a wheel, but don't expect much out of pCARS, Shift 2, things like that. I have no experience with iRacing though.
However, when it comes to Boot Camp itself, it's not just emulation software. The Mac becomes a PC, they operate in the exact same way, all Boot Camp really does (that you need to worry about) is install drivers onto the Windows partition so you don't have to worry about finding drivers for the integrated, proprietary hardware. That means you effectively don't have to worry about pretty much anything because it's not as if your hardware will be any different to Apple's spec unless you've got a Pro and replaced the graphics card with either an EFI-incompatible one (meaning it won't work with Mac OS at all) or a flashed, previously EFI-incompatible one (meaning it'll at least let Mac OS recognise it at boot, but support thereafter is sketchy) or something.
Aaaanyway, this is all a long winded way of agreeing with Jogo, just get the Windows OS that best suits the games you want. I suggest Windows 7 in any case.
good times!
