From the Ziff-Davis WHAT'S NEW NOW email newsletter:

NASTY BUG IN LATEST XP UPDATE SLOWS SYSTEMS DOWN

While rushing to get Server 2003 out the door, the Windows
team made a major blunder with its latest interim release of
Windows XP, which is automatically downloaded using the
Windows Update feature. Reports from all over the Web verify
that this latest version actually slows many systems to a
crawl. Ouch! We've got details on which XP version to watch
out for and how to get it off your system.

http://www.microsoft-watch.com/article2/0,...,1037305,00.asp

(This happened to my XP machine a few days ago when I installed the update, and I had noticed the slowdown ... I uninstalled the update today and my computer is back up to speed again. -- Dave Baker)