Guarantee/force remote shutdown
Have you tried to execute shutdown from Terminal:
sudo shutdown -h 2011032000 &quot;Shutting down at 8:00pm tonight&quot;

You can specify the precise time, using the yymmddhhmm format, and using a 24-hour clock for the time.
At least it doesn't ask me to quit or save any running program. It will simply quit anything running in.
You can make automator script to execute too if this helps for your requirement.