Upgrade and Installation information: http://kb.wisc.edu/wiscsoftware/page.php?id=12511

Potential Activation Issues when performing a clean install: http://kb.wisc.edu/wiscsoftware/page.php?id=12496

Can I do an upgrade install or must I do a clean install? https://secure.wikimedia.org/wikipedia/en/wiki/Windows_7_editions#Upgrade_compatibility