I think you're missing the point here. The upgrade version of Windows is only licsensed to be installed if you already own a previous version of Windows (I think from 98 onwards). It enforces this by checking for a previous version at startup. If you don't have a previous version installed, it asks you to insert a previous version disk. Once it's inserted and it's checked it's there and valid, then you'll be prompted to put the XP disk back in again and the install will be a full clean XP install - it's just a disk check, putting an old disk doesn't mean that the old version will ever be installed.
If you don't legally own a full version of Windows 98 or onwards then you can't use the Upgrade version, and you should return it and get a full retail or OEM version instead.