nah nah nah...its easy. you gotta log in to your local computer as local Administrator with unrestricted local rights. Then you use
shutdown -s -f -m \\computername -t 0
That should work in xp pro for sure, done it at school plenty. The only reason I can think for that not working is if you were trying to kick off an administrator on the computer you are attempting to shut off. Works fine at school on WinXP Pro.