Hope this helps someone else, been searching all day to solve this. Did a clean install on an HP with HP OEM xp pro sp3, when I went to update it MS said it did not have the latest service pack installled, which of course it does. To solve this I needed to download windowsupdateagent. Restarted and solved my problem now its updateing fine
This happened to me when I used a Dell OEM disk to reinstall XP sp3 on a Compaq using the Compaq key of coarse. The only time I saw an issue with update.