I reinstalled XP on my Mac recently. I'd bought the OEM version, as I was also buying a new hard drive and Microsoft's rules at the time allowed OEM purchases with non-peripheral hardware. Sadly, my mother had thrown away my COA with the product key. But no worries, ensured the lady on the phone; technical will give you a new one. I gave the guy on the other end of the phone the part number, and he asked "Who manufactured this computer, sir?" "Apple" "*chokes* who?!" "Apple" "But, Apple computers cannot run Microsoft Windows" "Yes they can, under Boot Camp" "Well, Apple does not install Windows" "No" "I see, so who manufactured the computer?" "Apple" "But they don't install Windows, they use their own system" "I know!" "So who made it?" "APPLE!" "I'm afraid I can't help" "I'd gathered that..." I called again, and Microsoft refuses to help me. To qualify for OEM software you now need to be a licensed system building company, not just to be building a system. Moral of the story, don't lose your COA. Carry on buying OEM software, but don't expect any help if it goes tits up.