sending instant messages to users

Hi

I want to make an application to send instant messages,
i.e if i am sending msg to any user , It should popup the message in that user's machine .

I want to know how to make application run as soon as the user starts his
machine , is it possible to get ip address of the machine using FMS.

Please give me some idea how to start my application.

Thanks in advance


regards
avanthika