Right click on desktop, create new shortcut.

Type shutdown.exe –i

Click next, type in name for your short-cut e.g. shutdown computers

Click finish.

Run the shortcut you just created. Now you can browse the network for computers to shutdown/reboot etc. or just type in the IP/Name of the computer.

You can even broadcast a message, and schedule the shutdown.

NOTE: You will only be able to shut down computers that you have admin access