You could spend ages researching that. And the fact that many people went from 32bit XP to 64 bit Vista just complicates things even more. Even now, the amount of people who think 'XP only sees 3.5GB but Vista sees the full 4GB' is pretty bad. I would just install the 64bit version and have done with it. Lifes too short to be reading up on something like that. I bet there is the odd game that runs slightly better on a 32bit OS but I reckon it would be an older game that is running at 200+ FPS anyway.