while im sure what dpk5e7 is saying answers the question (i havent used those commands myself), and is probably a very simple way to do it, ill offer what was my first thought when i read the question anyway.

it should be pretty easy to exec an external command, all you need to do is exec shutdown, using the command shutdown -s

if you type shutdown or shutdown ? in a command prompt it will give you all the switches you can use with it. for example you can set a delay (believe the default is like 30 seconds if you just do -s, you can also have it reboot -r or, my favorite, you can remotely shutdown a computer on the network using -m \\computername (good times

unfortunatly the message says where the command came from, but still can be fun

)

-Darth Simon