I don't know if you guys know this but the "upgrade" through digital river or win741.com or whatever is a actual retail copy and not an upgrade that requires a previous version of windows to be installed on your computer.
I sent out an email a few weeks ago asking this same question.
"Shopper Comments: I wanted to know whether this deal was for the full
retail version of windows 7 professional 64 bit; or whether this was for
the upgrade version of Windows 7 professional 64 bit which requires a
previous version of Windows Vista or Windows XP to currently be
installed on your computer?"
"Dear Customer,
Thank you for contacting the Windows 7 Offer online store.
We apologize for the confusion.
The Windows 7 offered in this promotion is a full version. You can
install this product even though you do not have a previous Operating
System installed in your computer or if you want to make a multi boot
using Windows 7. The "Upgrade" included in the product name is just
because Windows 7 is the latest Operating System Windows developed.
For more information please contact our pre-sales department at:
1-800-642-7676
Sincerely,
Isidro M.
Windows 7 Offer online store
Customer Service
[email protected]"