Restrictions on Windows 8 in-place upgrades detailed
 

Windows 8's retail release is fast approaching. Unless the new Metro user interface gives you a rash, you might be thinking of upgrading—and an in-place upgrade would be the least painful way to do that. Well, ZDNet has gathered some helpful information about which past editions of Windows will support in-place upgrades to the new OS. The information isn't strictly official, but it should be legit. It reportedly originates from "select" Microsoft partners who were briefed by the software giant earlier this month.

http://techreport.com/discussions.x/23187