Define the commands to shut down or restart the computer. The shutdown command defaults to:
/sbin/shutdown
The restart command defaults to:
/sbin/reboot
Define which session types should be accessable from the login window. If you don't know what this meens have a look at /etc/X11/xdm/Xsession or whereever your xdm setup files are and look at the xdm man pages in the SESSION PROGRAM section