Microsoft is communicating via Dutch press release their official method of doing a clean install using upgrade media of Windows 7. The press release only mentions Vista and XP as legitable upgrade OSes. It’s same method that worked with Vista and involves installing it twice:
- Do a clean install of Windows 7 using an upgrade installation media (DVD/USB)
- When installation is done, do not activate it, as it will not accept your product key.
- Within 30 days (or before activating is required) do an upgrade installation again of using Windows 7 upgrade media (DVD/USB).
- Now you will be able to activate Windows 7 using your product key