http://www.windowsitpro.com/mobile/p...D=95011&News=1
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.
6. Install Vista normally.
7. Once the install is complete, restart the DVD-based Setup from within Windows Vista. Perform an in-place upgrade. 8. Enter your Product Key when prompted.
This is what I found at this web site. Don't know if it works!