De acordo com este artigo , você precisará ter uma cópia ativada do XP, Vista ou 7 RC primeiro:
Now here's the bigger catch: While you won't need to downgrade from Windows 7 RC to Vista or XP in order to install Windows 7 final the first, time, you will need to install one of those operating systems and activate it first if you want to do a clean install in the future. Because the Windows 7 upgrade disc will only work with an activated version of Windows. That means you'll need an activated version of Windows XP, Vista, or Windows 7 RC to start with or the disc will be useless.