windows/7 : legal copy ?

how can i find out if the used desktop gaming computer i'm going to buy has a legal / non-temporary copy of windows/7 on it ? the guy i was going to buy the computer from said he installed windows/7 , using a friends copy and did not use the product/activation key, he said there's a 30-day trial period, now he says he's loaded an unofficial activation code and the warning about the 30-day grace period is gone, that there is no problem now: how can i check to make sure windows/7 won't become disabled at some future date ? thanks

 

You were specifically asked by a forum moderator not to raise this issue again.

 

From your description, you know you don't need to check if it's legal and you can count on MS fixing the problem for you. Figure in the cost of buying a legitimate license and buy it if it's still a good deal. I advise you not to ask again. It won't change the answer.