Do you mean Sp2? There is no Sp3 yet for XP. You shouldn't need a disk, you can get the update online through Windows Update. If you are prepared to deal with the setting changes (Google XP service pack 2, you should be able to find some pages on what it changes, and how to make sure everything works afterward), it is a recommended update that actually takes some pretty large steps towards making Windows secure.
Service Pack 3 is for Microsoft Office. It was released in 2002.