As long as you have vista installed, or a vista disk, you can do a upgrade to the same version of Windows 7 from vista. And you can do a clean install from the disk, without clean installing and then activating, the upgrade doesnt necesarrily mean you have to do an upgrade, it means you had vista before. vista made you put in the xp disk if xp wasnt installed and then it did a clean install of vista and all was good.