Information tidbit coming (indirectly) from Microsoft. It is possible to install a Vista upgrade even without having a previously installed Windows (it is quite interesting because of the tremendous price difference between full Vista and upgrade Vista). Apparently, according to Paul Thurrott, you only have to follow the steps:
- Boot on the upgrade Vista DVD
- Click on “Install now”
- Refuse to give the license number when asked for it
- Tell the Vista kind you bought (when requested by the install software)
- Finish install normally
- Restart the install program from the Vista upgrade DVD, as soon as the first install is finished
- Do a normal in-place upgrade
- Give your license number when requested
The Microsoft license does not agree with this (you are supposed to already have a Windows license to use an upgrade Vista DVD), but it is documented internally at Microsoft, seemingly.