So I went to activate windows today and chose the 'over the phone' option expecting to have to explain the situation to a representative - I keyed in the number that it asked me for (the massively long registration number that gets generated on your pc before-hand, when you put your windows SN into the activation box prompt), and then the robot voice lady gave me a massively long activation key which resulted in the end of the call. I put the activation key I was given in and it activated the copy of windows no problems what so ever, despite this copy having been previously used.
Now, it was last used 6 years ago, so is there some kind of automatic reset/redeem after a certain period of time that allows you to use it again? (as once X number of years have passed it's pretty obvious you're not trying to install it on every computer in sight?)