I recently upgraded two of my home computers to Windows 7. One of them was already running the release candidate version of Win7, and the other, our media center PC, was running XP. The media center was treated to a clean install of Win 7, courtesy of an Upgrade version of Windows 7, which is cheaper than the full version, but my plan to save a little money ran into an unexpected snag: the clean install wouldn't activate with the enclosed key, primarily because it was a clean install.