Yes, because it's going to wipe that installation anyway. All the upgrade is looking for is that you have qualifying media to use the less expensive upgrade media. There is no build upon.
I assume you meant, qualifying installation, since it does not ask at no point during the installation for the XP or Vista media. It does say on the Upgrade DVD that your hard disk will be searched to confirm your eligibility for this upgrade.
Andre Da Costa http://adacosta.spaces.live.com http://www.activewin.com