No need to buy a license, I'll put in simpler terms. Oem machines have what they call a slic table embedded in the bios. Depending on the year of the machine some tables have both vista and 7 licenses. The key is that you have to have a oem disk to upgrade it with. For instance I'm sure you remember doing a reload back in the day on a dell machine with a windows 7 dell disk. If you remember, did ever have to put a product key? No because if you used the oem disk and it would just activate. Same difference with a upgrade. First I checked the oem slic first to see what licensing it had. Then if it had 7 then I would do the upgrade. Like I said before, pain in the a$$ to do.