Yes, you can use the product key number from TechNet to activate only the Windows 7 edition that the key is for. For example, you cannot use a Home Premium key to activate Ultimate, or the other way around.
Since you have a TechNet or MSDN subscription, you can easily download the edition you want to install and get a key number for it. If not, then it is illegal until you purchase it on October 22nd from a retail store.
Hope this helps,