Where to buy Windows OS 7

A location might be helpful, but you are not going to find windows very cheap through a legit seller. While there are a few places that sell cheap keys they are usually not legit like generated keys, MSDN keys, or keys taken from dead OEM units, neither is suppose to be resold and when microsoft finds out the keys will be deactivated.
 


I live in UK
 


Can i just ask if you can tell me how to transfer that to a USB because i dont have a DVD drive