http://labnol.blogspot.com/2006/04/w...n-genuine.html
This link should help you disable that POS Update.
Some preventitive medicine:
1. Manually update, do this by telling Windows to notify but don't install or download updates. Also hide any Windows Genuine Advantage related updates you find so you don't absentmindedly install them (though you might have to install some of these to update).
2. If your copy of XP is legit, then call Microsoft and have them sort out the problem. Remember, only do this if you get this shit pop-up with a legit copy of WinXP
3. Download
this file and extract it to the [systemdrive]:\Windows\system32\ folder and overwrite the "LegitCheckControl.dll". Check 9down.com every once and a while to get a newer version of this file so it can disable WGA checks. If you have an illegal copy of WinXP, you'll be able to do manual updates now.
A hassle for sure, but if you have a pirated copy, it's what you have to do. In fact it's better than some of the other cracking programs out there since Microsoft isn't trying to disable your OS if it's pirated (we'll see how they do this with Vista).
Jam it back in, in the dark.