That's the correct link:
Windows XP Service Pack 3 Release Candidate 2 via Windows Update (released to the public by Microsoft on 2008.02.19)
Once you run that, you can download SP3 RC2 from Windows Update.
I think you might be getting confused on the "release candidate" terminology. Basically, this is like an extended public beta test before SP3 is released as SP3 GA ("general availability", which will just be called SP3) later this year.
AHHHH - thanks! this is very helpful...