To all you pirate windows xp users out there, tried using windows update lately? Well it's no longer available to you. You see with the introduction of service pack 2 for windows xp, Microsoft have decided to stop pirates from getting the security benefits of their product. Despite rumours that microsoft would loosen security with service pack 2, but it isn't surprising that they've taken the same stance that they did with good ol' service pack 1. Windows update now checks your Product ID with a list of activated product ID's and known pirate product ID's. If you are in the list then, no updates for you! If you have got your own legal copy of windows however, and it still wont let you update, my advice would be to contact microsoft ASAP. Chances are a pirate has allready used a program that generates Product ID's based on the algorithm microsoft used. It is rare, but I have heard cases where this has happened.
Read Larry Seltzer's article "Do pirates deserve a windows update?" here.