Shutting down computer with GPO

I am trying to create and push a batch file to shutdown computers at a specific time at night on a domain network using a Windows Server 2008 R2 with SP1 installed.

I have a mixture of both XP, Vista and W7 machines.

For example, I have read using psshutdown in the following manner works:

psshutdown.exe -s -f -t 21:00 -m "regular shutdown" \\pc-name-1,pc-name-2,pc-name-3

Where do I place the batch file to run?  Do I create a new GPO for it or do I push it using the log on or log off script?  Is there another way to accomplish the same thing besides using the task scheduler?

Thanks in advance.