To help you all work out what you can and can't upgrade from:
Windows 7 Upgrade Chart
Printable View
To help you all work out what you can and can't upgrade from:
Windows 7 Upgrade Chart
Might want to think about pinning this for a while.
I know this is not exactly about upgrading choices but it does tell you about how to make a choice from the many & various versions out there.
http://www.winsupersite.com/win7/review_choose.asp