client log off question

hi, new to this forum and c#, so be gentle Im writing a simple client server program, basically the server listens for the server to send it messages, SIMPLE! Now what i would like to know how to do is........ for the client to open up as soon as the computer is logged on... and send a message to the server when it is logged off. this will enable to the server to know who is logged on any code, tips or tutorials would be greatly appreciated cheers!