"Factory Reset" of Vista free upgrade to Win7

The WIndows 7 'free Upgrade' is a standard OEM System Builder Key - and as such it will work fine with either OEM System Builder disks, Retail Disks, or the downloads from Digital River.

Well, to get a clean install, get a clean install. It goes for Windows as well as for a Ford or Mercedes engine. The only way to get pure is to use soap = start from nill, period. Upgrading Windows has always been a risky procedure, starting from zero is far better. Get the disks, install from them, that way you have it all PLUS you have full support from Microsoft. And guess what - you may breathe freely!