I have a Snow Leopard Server in production use and do not wish non-administrator users to be able to select "sleep", "restart" or "shut down" from the apple menu. I have had users who are used to shutting down their workstations at night, just create chaos when they have shut down the server rather than logging off.
Sorry guys for digging up a tiny bit of an old post but I too was hunting around for ages until I began to actually learn something about osx server. I am using the latest lion manifold so I am unsure if the exact procedure will be the same for SL.
2 words, "Workgroup Manager".
The settings you are after sit in Preferences(either the icon at the top next to Accounts or view==>preferences next to file menu)==>Overview/Finder==>Commands.
I suggest creating groups to manage what you are about to do effectively and segregating admins from non admins as a root group and spanning from there.