Ok, it’s a trick question. Take a look at the following exchange.
You should activate an operating system once. Due to the OEM scandals and widespread piracy, Microsoft came up with WGA which has done little to prevent piracy, but a lot to annoy legitimate users. You can see Susan’s discussion above and you should be aware of it too:
When you install Vista SP1 and it patches certain drivers (change in hardware) it will require a new activation.
Which is OK, fair enough, making sure the OS hasn’t hopped from box to box. Click on the link, activate over the Internet, back to business. Unless you use MAK or OEM – in that case you get a warning that your copy of Vista is not legitimate and you’re given a three day Window during which you must convince an IVR and some sweatshop blue badge that you indeed are a legitimate customer. So if you manage Vista deployments, get ready to annunciate installation GUIDs over the phone for all your Vista deployments.
This may be the first time in recorded history that a pirated copy of an operating system is actually less of a hassle than the legitimate version.