Remotely Shutdown other user's computer who are connected in the same network.

Go to RUN -> CMD
Type: shutdown -i. A remote shutdown window will appear.Now enter the usernames in the box.You can directly add or browse the user names.
Choose the appropriate choice from the list i.e shutdown,restart or in appropriate shutdown.Click OK

Note:According to my experience,this will not work in the networks where there are network administrators. I have tried this in my college network and failed.
But it works in the home and office networks.Try it and let me know if anything works for you.