Well as Far as i Know Replying to the original question you can install it only on one comp {Microsoft registration scheem" thier might be away around it *hint hint*, or if u have the corporate eddision depending on what type of contract u have with msn most of them are for 100 computes wich eqaul 100 diff activations on diff computers and if u can get ur hands on one of those ur a lucky man, lol