I'm trying to theoretically work something out for Windows 7. Please answer my question: If I had an OEM Windows XP Professional product key, and I then installed an untouched version of Windows XP Professional with Service Pack 3 from July 2009, would I be able to activate it with that same product key?
Only with a modified BIOS or a lo*der that injects the necessary credentials into memory before booting XP. None of this is very tough and is explained in the XP forum. You can even convert a currently installed non-OEM in-place without reinstalling. It's time for some reading in the XP forum...