This is the easiest way you can shut down your friend's computer while you are chatting with him.
1. Open your note pad.
2. Click on file.
3. Click on save as.
4. Name the file "shutdown.bat".
5. After the file is saved send it to ur friend's computer while chatting or as mail.
If your friend accepts the file transfer or downloads this file sent then his/her computer will automatically shut down.
Try it and enjoy.