for MSDN subscriber, you can download Windows 7 RTM at MSDN Site for the different between windows 7 edition, you can read here : http://en.wikipedia.org/wiki/Windows_7_editions too bad, my MSDNAA can only access Enterprise Version not Ultimate version...
it released a month ago, but I just realize there's SP 1 for WSS 3 download : http://www.microsoft.com/downloads/details.aspx?FamilyId=EF93E453-75F1-45DF-8C6F-4565E8549C2A&displaylang=en "just" 104 Megs :D (now downloading ...) for change...