Group Policy to remove Hibernate and Sleep from the start menu

Hi, I have been looking for the past week to successfully disable the hibernate and sleep buttons ONLY, on the start menu for my users.

I am using Server 08 R2 and Windows 7 clients. From what I have been reading, this was an issue with server 2003 also. Surely there is a simple group policy somewhere for this in 08R2?

Any help would be greatly appreciated!

Thanks 

Matt