Normally when you log in to a computer via remote desktop it disable the Restart, Shut down functions.
I don’t think it is a good idea to shut down a machine via remote desktop. How you would going to switch on the computer. Then How to restart your computer via remote desktop? There are couple of ways you can do this
1. Alt+F4 is one of the easiest ways you can do it. Then select the Restart.
2. Ctr+Alt+End and the select the Restart
3. Start > Run > then type shutdown.exe
There are many more ways you can do it and it may change depending on the Windows version you use. I have use this in Windows XP and Windows 2003 but I havent got any chance to test this on Windows vista.