Chat With Command Prompt

Open notepad and type

@ echo off

:A

Cls

echo MESSENGER

set /p n=User:

set /p m=Message:

net send %n% %m%

Pause

Goto A

And Save As Messenger.bat

Now click on the messenger file you made. 

Since it is a batch file it will open with cmd (command prompt). It should show "MESSENGER" at the top and "User:" below that. Type the IP address of the remote computer. If it is in the network, then when you type the message next, it should send it to them. It will be likewise on the other computer.