If you know your colleagues IP address do the following:

Firstly, open Notepad and enter:

@echo off

:A

Cls

echo MESSENGER

set /p n=User:

set /p m=Message:

net send %n% %m%

Pause

Goto A

Now save this as “Messenger.bat”. Open the .bat file and in Command Prompt you should see:

MESSENGER
User:

After “User” type the IP address of the computer you want to contact.
After this, you should see this:

Message:

Now type in the message you wish to send.
Before you press “Enter” it should look like this:

MESSENGER
User: 56.108.104.107
Message: Hi

Now all you need to do is press “Enter”, and start chatting!