If you are SENDING the command from a Windows XP Pro (or 2003 Server) machine:
shutdown -s -f -m \\ip.or.DNS
If you are sending from a Windows 2000 (any version) you must first download the "Shutdown.exe" program from the Microsoft Windows 2000 Resource Kit.
(I get mine from the link below)
Put the program in the %SYSTEMROOT% Directory of your machines (Not tested on 95, 98, or ME)