SMS 2003 - Troubleshooting - Another Update on the Classic CPU Spike Problem
I won't bother regurgitating the details on this problem as we've all probably experienced it. Here are the links: (Updated May 22, 2007)
http://support.microsoft.com/kb/927891
http://support.microsoft.com/kb/932494
http://support.microsoft.com/kb/916089/