That's one method, but not the one I'd recommend personally. Simply because it advises you to turn off Windows Update and that's a big no-no in my book. There are plenty of beneficial updates that come from Windows Update. Unfortunately you also have to deselect it every time you do a Windows Update with that method as well, because it will prompt to re-download it.
My method is not allowed to discuss on the forums.
But if you want to find out once and for all if your copy is genuine, you can simply go to:
(you need an account to see links)
Be prepared though, generally if it is detected that it is not genuine, you aren't going to be able to reverse it without following one of the methods listed by Graff or the one I can't talk about publicly.