if all you are trying to do is write a script to reboot or shutdown those fifty machines, i dont understand what users have to do with it. If you have an account that has the right on each remote machines to reboot the wks, then you should be able to reboot them with the 'shutdown.exe' file. I use 'shutdown.exe' from the NT Resource kit, (I just like the syntax better than the newer versions, and I issue the command like such:
shutdown \\machine /Y /R /C
where /Y = Yes
where /R = Reboot
where /C = means automatical close any running applications
HTH - Please give more details