This is easiest done with a Group Policy. Make sure that you use
"loopback processing" of the GPO, otherwise you will remove the
Shutdown option from the local clients Start Menu as well.
And you don't need to use a vbscript to let Administrators reboot
the server, you can simply deny the Administrators the right to
"Apply this policy" (if in a AD environment). Or bring up the
standard security dialog and reboot from there.
Note that removing the Shutdown option from the Start Menu is a
cosmetic thing only: normal users don't have the right to reboot
the server, even if they see the Shutdown option. And vice versa:
if you remove the Shutdown option, but users have elevated rights,
then they will still be able to shutdown the server (from the
command prompt or the Security dialog).
278295 - How to Lock Down a Windows 2000 Terminal Services Session
http://support.microsoft.com/?kbid=278295
260370 - How to Apply Group Policy Objects to Terminal Services
Servers
http://support.microsoft.com/?kbid=260370
231287 - Loopback Processing of Group Policy
http://support.microsoft.com/?kbid=231287