I'm using Win 7 x64 and initially installed by the Upgrade method. The only area I had any difficulty with was networking... my adapter would "drop out" randomly and Win7 would attempt to reset it leading to a computer lock up. I won't go through all the details in this post, but let's just point out that one of the suggested repairs may be to Clean Install Win7.So, that is what I just accomplished.What changed? Well, the USB adapter still drops out randomly. My wireless connection states Excellent connection, yet downloads are severely limited in speed. I've tried the MS driver and the vendor's driver. Neither improve the situation for either network card.As a side note, the upgrade had no problems incorporating my coprocessors and audio devices. (It accepted existing drivers without a problem.) The clean install could not figure out what they were and subsequently could not download any drivers. When I did install the drivers, I was provided warnings they were not signed! This included WHQL nVidia drivers, which are signed.Bottom line:Yes, there is a difference between an Upgrade and a Clean Install and the later is not necessarily better.