Click Start | All Programs | Accessories | System Tools | Scheduled Tasks | Add Scheduled Task
Click Next | Browse, type in:
%windir%\system32\shutdown.exe
and press [Enter].
Select "Daily", (or whatever), and click Next.
Pick a start time (say 9:00 PM) and click Next.
Type in the password (twice) for the username displayed and click Next.
Select "Open advanced properties for this task when I click finish" and click Next.
In the Run: box, add the following parameters to the end of the line:
-s -t 0 -f
(Note: Be sure to leave a space between the "shutdown.exe" and the "-s").
Click Apply and a pop-up will appear prompting you for the password again. Type it in (twice) and press [Enter].
Click OK.
You should now see your new "shutdown" listed in your "Scheduled Tasks" window. (Note that you can right-click and rename it ... maybe something like "Forced Shutdown at 9PM").
To remove it, simply right-click it (in Scheduled Tasks) and select Delete.
Important Note: The Windows username you are setting this up for must use a Windows logon password ... even if it's something extremely simple, like a "1".