Windows Vista Upgrade Secret

The "secret" is that the setup program (setup.exe) in Windows Vista's upgrade version will accept an installed copy of XP, W2K, or an un-activated copy of Vista itself as evidence of a previous installation.
This last option that enables you to perform a "clean install" off an upgrade version of Windows Vista to any formatted or unformatted hard drive! Basically you are installing Windows Vista twice to take advantage of this trick.