Mac OS X Lion Server: How to disable Sleep/Restart/Shutdown options for users?
I've removed shutdown for my lab Macs on OS X Lion. The two commands that should accomplish this are:

sudo defaults write /Library/Preferences/com.apple.loginwindow ShutDownDisabled -bool true
sudo defaults write /Library/Preferences/com.apple.loginwindow ShutDownDisabledWhileLoggedIn -bool true


I've not had 100% success with them, so I've also edited the interface file at: /System/Library/Frameworks/Carbon.framework/Versions/A/Frameworks/HIToolbox.framework/Versions/A/Resources/English.lproj/StandardMenus.nib/objects.xib

If you want to remove the Sleep and Shut Down options, look for the following id's in object and reference tags. Delete the entire object, one for the Sleep option and two for the Shut Down option, and each of the references.

id's:
Sleep - 236
Shut Down - 238, 285

Source: http://rustyisageek.blogspot.com/2012/06/editing-apple-menu.html

Edit: I've been told that when these settings are applied with MCX, they work as expected!