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.

Kill Switch in Windows Vista

Microsoft's efforts to combat software piracy is stronger with Windows Vista than they are with XP. Vista will virtually disable your computer if your Vista install doesn't pass Microsoft's validation test. At one point, people using a failed copy of Vista will not lose access to their personal data. Instead, they will see a persistent message on the desktop telling them the copy of Vista isn't genuine and they will lose access to certain Vista features.

Windows Aero
Windows Defender
Windows ReadyBoost
Download Center
Windows Updates