Client to Client chat

Hi ,
I am new to c# . I want to develop a simple lan messenger which shud be something like "ip
messenger" . where you dont need any seperate server. Please guide me how to acheive this.
It shud be a single exe file which on opening shud list all the connected people (ppl who
opened this exe file on another machine , instead of all those who are connected in lan).
The user shouild be able to select the user he wants to send message .(not to mention shud
ber able to recieve messages)
I have gone through many lan messenger tutorials but din't find one which doesm't use any
server like ip messenger.  Thanks in advance :)