Can anyone show me how to chat with people in a Lan network.
Any software is so good.
Thanks.

You have 3 options:

Just use an instant messenger like MSN Messenger. This is what I find most companies do internally.
Use commands like net send (http://www.microsoft.com/resources/documentation/windows/xp/all/proddocs/en-us/net_send.mspx?mfr=true) but these aren't built for having a conversation.
You could try running your own chat server which people on your LAN could connect to. Here are some examples which would need Java to run
(http://java-source.net/open-source/chat-servers)