Why should you be able to do a clean, meaning "from scratch" install with an upgrade DVD? I might ask, why not? As long as you can prove you owned a valid copy of a qualifying version, in the form of either an activation key or a valid media, it seems fair. However, that sort of "deal" ended with Windows XP.
Windows Vista required you to basically install the OS twice, to get a clean install with upgrade media. I can attest to the fact that it worked.
For Windows 7, Paul Thurrott has discovered a way to cut some of the time off a clean install with upgrade media. Although the old "double install" trick should work, this saves you a ton of time. Here's how it works:
- Do a clean install.
- Ensure that there are no Windows Updates pending that would require a system reboot. (You'll see an orange shield icon next to Shutdown in the Start Menu if this is the case).
- Edit the registry with regedit.exe. Navigate to: HKLM/Software/Microsoft/Windows/CurrentVersion/Setup/OOBE/
- Change MediaBootInstall from "1" to "0".
- Open the Start Menu again and type cmd to display a shortcut to the Command Line utility. Right-click this shortcut and choose "Run as administrator." Handle the UAC prompt, if any.
- In the command prompt window, type: slmgr /rearm [ENTER]
- When Windows 7 reboots, run the Activate Windows utility, type in your product key and activate Windows. You are now gold.