From "Making Windows XP Start Faster" at,1759,1768883,00.asp

Two of the services listed under "Stopping Unneeded Startup Services"
  • Automatic Updates: This service enables Windows XP to check the Web automatically for updates. If you don't want to use Automatic Updates, you can disable the service. You can always check for updates manually at the Windows Update Web site.
  • Windows Firewall/Internet Connection Sharing: If you do not use these features, you can disable them.