Windows XP/2003/Vista/2008/7
Windows Registry Editor Version 5.00
;Kill hung programs after 5 seconds
[HKEY_CURRENT_USER\Control Panel\Desktop]
"HungAppTimeout"="5000"
"WaitToKillAppTimeout"="5000"
;Kill hung services after 5 seconds
[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control]
"WaitToKillServiceTimeout"="5000"
With this tweak your system shouldn't have any trouble shutting down.
-Shane