Andrew,
I am not very window savy, but, I have a Widows seven that is a legal copy, that is installed on my dual boot Windows Linux machine. This is a recent installation, last month, I was able to upgrade to the most recent service pack, automatically, despite having received the Microsoft no longer supported message! I didn't need need to enter the registration code! I hope this is helpful, I know you know Windows 7 far better than Ido!
Cheers Matthew.