it doesn't require any previous windows key. You just have to install it twice. You do a fresh install, not worrying about activating or putting in your key. Then from the desktop of your freshly installed windows 7 you put in the disk again and run setup from your desktop doing a fresh install again, fooling it into thinking you're upgrading from a version of windows since you're starting from your desktop. Do a "custom/clean" install again, and this time, your 2nd time through you put in your key etc.