How can I update from xp pro (with slipstreamed rtm sp3) to the release sp3?
I can't see how to uninstall the rtm sp3.
If what you currently have is rtm SP3, that *is* the release version
(rtm means *Released" to Manufacturing) and there's no update
required.
On the other hand, if what you actually have is an RC (Release
Candidate) version, you now need the rtm version instead. To get
there, you need to uninstall the RC SP3 first. However if you
installed it from a slipstreamed CD, it's not possible to uninstall
it, and you'll either need to restore from an image backup, if you
have one, or else reinstall Windows cleanly.