Windows enthusiast Paul Thurrott has published a possible, but yet-to-be-confirmed, workaround for Vista's new upgrade requirement. It's still not too pretty, but it allows you to install an upgrade copy of Vista without dealing with older versions of Windows.

1. Boot with the Windows Vista Upgrade DVD. 2. Click “Install Now.” 3. Do not enter a Product Key When prompted. 4. When prompted, select the Vista product edition that you do have. 5. Install Vista normally. 6. Once the install is complete, restart the DVD-based Setup from within Windows Vista. Perform an in-place upgrade. 7. Enter your Product Key when prompted.