Save yourself hassle. Download the FULL SP3 and apply it instead. Grab the one that the IT guys use.
http://www.microsoft.com/downloads/d...displaylang=en
I've heard ppl have had issues with using the "lite" installer that MS is using from WU. Certainly everyone who updated using the full installer avoided the annoying issues that accompanied the inital push from MS.
Plus you can then slipstream SP3 into your XP cd and just reinstall from that instead of a unprotected XP CD. Its worth the hassle.