A member in the Tweakers Australia forums found a little hack, actually a registry edit that is supposed to speed up the Windows XP shutdown / startup command by altering the WaitToKillServiceTimeout key. "My Windows XP took up to 30-45 seconds to shut down until I found this tweak and WOW! Please back up your registry before making any changes. Go to Start -> Run and type "regedit". Navigate to "HKEY_LOCAL_MACHINE/SYSTEM/CurrentControlSet/Control" click on the "Control" folder In the right window you will see this key "WaitToKillServiceTimeout" Double click that key and set it to a value lower than 2000. I set mine to 100 then Rebooted." Source Link: Tweakers Australia
Direct Link: Windows XP Shutdown Hack