Product key & activation lost when upgrading OS?

I've just upgraded my Vista Business notebook to Windows 7 Professional. It had NIS 2009 on it, with about 185 days of subscription remaining, and it was the third of three PCs on this subscription.

 

Now I'd like to reinstall NIS 2009 and reactivate the remaining 185 days of subscription. Is that possible or do I have to buy a new product key?