It seems some computers will not boot back up after installing KB929338. If you are not experiencing the problem described in the update do not install it.
Update for Windows XP (KB929338)
Typical download size: 725 KB , less than 1 minute
This is a reliability update. Install this update to improve the stability of computers running Windows XP. This update prevents some Stop 0x1a or Stop 0x0a errors. After you install this item, you will have to restart your computer.