It's easy - and you need install Windows only once.
Basically two little things one must do - a regedit and a commandline
First install Windows clean with the upgrade disc BUT during the install
routine DO NOT type in the Product Key and DESELECT the Automatically
activate when online checkbox.
Once Windows is installed, do the regedit:
- navigate to
MediaBootInstall from "1" to "0".
Then do the commandline:
- At a Cmd Prompt type in:
- then hit Enter
- Close the Cmd Prompt, click any OKs and then reboot.
You can now activate through the System applet found in the Control Panel.
Paul Thurrott has it all documented with screen shots on his WinSuperSite:
[Clean Install Windows 7 with Upgrade Media - WinSuperSite]