How to disable the option?

[raiden]

Hi, Um, I need to know, if i can remove the "turn off
computer" option which appear in the welcome screen.
because i do not want normal users to have the ability to
shut down or restart the computer. i have removed the
shut down tab in their start menu, but the problem is,
when they log out, they can still shut down the computer
by the option in welcome screen. so please tell me how to
do that. thanks
..