I am looking at getting W7 for another one of my computers. I have never really had to buy my software before because my sister in law worked for Microsoft and I got it for free. She has since went on to another job and I don't get those benefits anymore. So I now am faced with buying W7. Should I buy OEM or retail. I know OEM is cheaper but what happens when something goes bad and you have to put in a new part. How is MS about dealing with this?