I did a search and didn't find any results concerning this problem. I've just built a new system and my Windows 7 disc won't boot, so I'm installing Windows XP so I can then install Windows 7 on top ...
In general, having the product keys for your Microsoft products is a good idea. The easiest way to grab those product keys is from the product box, or in the case of Windows, from a sticker on your PC ...
I have a friend with a desktop machine that had Windows XP Pro on it. She formatted the drive with some other version of Windows, but not before I took screenshots of the original Windows XP product ...