Very often I must perform a repair install or clean install of Windows XP without knowing which version it is. Obviously, I know if it is Home or Pro or MCE2002 or MCE2005, but I often don't know if it is OEM, retail, corporate (open license), or a special Dell/HP/Sony-specific one that I occasionally encounter. If the XP sticker is on the computer it's usually OEM, but otherwise I don't know how to tell which version it is. If I use the wrong version of Home or Pro to perform a repair install or clean install, then obviously the product key doesn't work with that installation. How can one tell, from the product key or otherwise, EXACTLY which version of XP is installed on a machine?