I'm finding out that a LOT of readers of this site are using illegally obtained CD Keys and will not be able to install XP's service pack 2 (SP2). Since you can obtain COA license's really rather cheaply I highly suggest you purchase a license and then use this tool here to change your CD Key.

Here's what the program looks like. All you have to do is type in the new Product Key including the -'s

If for any reason you've forgotten your CD Key and misplaced your COA sticker then you can use this application here to view what your CD Key is.

Now you little pirates have no excuse to NOT upgrade to SP2 when its released. I believe MS is planning on blocking quite a few additional known pirated keys by time SP2 is released.