I only know how to prevent other users from turning of the computer at all.
if you have Windows 7 (or probably Vista, maybe XP) in a flavor that has the Local Security Policy Editor (W7 and Vista - Ultimate, Enterprise, Pro. XP - Pro)
open 'Local Security Policy' (in Administrative tools, either in control panel or in start menu)
under 'Local Policies':
under 'User Right Assignment', change 'Shut down the system', by adding/removing users/user groups that you want to be able to shut down the computer.
under 'Security Options', change 'Shutdown: Allow system to be shut down without having to log on' change to enabled.