Well this is a big disappointment. It seems if you purchase any of the Upgrade versions of Vista, which are cheaper than full retail versions but requires you to have a valid Windows 2000 or Windows XP license already, you won’t be able to load the upgrade on an empty hard disk. Otherwise known as doing a clean install:
What does all of this mean on a practical level? Users who purchase upgrade copies of the aforementioned versions of Vista will find that they can only upgrade PCs that already have Windows installed. KB930985 clearly states: “you cannot use an upgrade key to perform a clean installation of Windows Vista.” According to Microsoft, this happens because Windows Vista does not check for upgrade compliance. If you do not have a previous installation of Windows available, Microsoft recommends that you “purchase a license that lets you perform a clean installation of Windows Vista.”
For its part, Microsoft seems to be confident that the Vista repair process should be sufficient to solve any problems with the OS, since otherwise the only option for disaster recovery in the absence of backups would be to wipe a machine, install XP, and then upgrade to Vista. This will certainly make disaster recovery a more irritating experience.
Fortunately, the change will not mean that users cannot install Windows Vista to a new directory. Windows Vista’s upgrade process includes the option of backing up previous installations, and in fact, in some scenarios a “clean” upgrade is required. “Clean” or not, the requirement that the previous OS be installed puts a bit of a damper on those of us that like the do periodic system refreshes.
As someone who periodically restages his PC this is rather annoying. Fortunately there’s always the OEM route which tends to be cheaper than a standard retail license anyway and isn’t affected by this change. Still it’s something to be aware of if you’re considering purchasing any of the upgrade versions of Vista.