This makes it even less clear for me because it appears you can use the upgrade version on a clean system: http://windows.microsoft.com/en-us/windows7/Installi

This makes it even less clear for me because it appears you can use the upgrade version on a clean system: http://windows.microsoft.com/en-us/windows7/Installing-and-reinstalling-Windows http://windows.microsoft.com/en-us/windows7/Installing-and-r...