What he said... Halo 3 is going to sell systems for MS and be their biggest weapon in the console war to date. You won't see that on another system for years, if ever.
XBOX 360 is the only way to go for Halo 3, it took MS two years(and two extra weeks) to get Halo 2 to PC. Halo is a console game, it's not designed with the PC in mind. I beet it takes probably three years for this Halo to get Vista'd.