Right click on desktop, create new shortcut.
Type shutdown.exe –i
Click next, type in name for your short-cut e.g. shutdown computers
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