I got the microsoft update for Windows XP (service pack 3) on my desktop this morning. It kept restarting and restarting all day. Finally I stopped it and had to recover my hard drive.
Take it easy guys, jmcole is right. This is a known bug, but seems to affect only HP machines with AMD processors. There appears to be a fix by going into SafeMode and changing a registry setting. Just Google to find exact fix.
Thanks again DFL. I chatted with HP on my laptop (since the desktop was inop). They gave me the fix for the problem, SP37394.exe. I had to uninstall the sp3, run the fix, then reinstall sp3. It works great.