I had WinXP on an older drive, then I upgraded to Vista 64bit, then the disk crashed. Got a new hard drive and installed just Ubuntu 11.04 on it. Then I missed Windows and decided to get a Windows 7 Upgrade. I thought that since I had the XP product key/sticker (on my Thinkpad T400) AND my Vista 64bit Upgrade (with product key) AND my new Windows 7, I'd be set and legal.
First, the Windows 7 upgrade DVD didn't like seeing the Ubuntu partition and didn't want to install. I popped out the drive, put it in a external caddy and had my other XP machine format it as NTFS. Good. Reinstalled HD and put in the Windows 7 64b DVD and installed Windows 7. Everything went fine untill the Product Key . . . which it would not accept! This is a legit copy I just bought at WalMart, but it wouldn't accept the key! I finally clicked on "Skip" . . . and it went on installing, upgrading and appears to be working fine! What gives? It didn't ask me for my old Vista copy or key, it simply went on and seems to be working fine. I'm using it right now. (Having trouble getting it to see my external monitor, but that's another thread. . .)