I also get a similar thing, when logging in it only gives me the option to buy the premium upgrade and not the pro upgrade.
Hopw do you go about getting the pro version?
Direct from Microsoft:
To place your new order, please locate your eligibility email
confirmation and follow these instructions:
1. Click the link and log in to the store.
2. Locate and click on the yellow box with the statement " Need to
join your school?s network domain? You can also get Windows 7
Professional. Click here."
3. Select the version of Windows 7 Professional you wish to purchase
and complete your new order.