Hi,
How long is a piece of string? I assume from the location of this posting you are looking for a solution to an application you intend to write.
With this said you have to take a few things into consideration, like how many clients there would be at maximum. Can these clients talk to any other client? How are the messages to be routed? Can a client send a message to more than one other client? Where do you site the server if you have one, etc.
But in it's simplest terms the answer (for me at least) would be to use Sockets (see MSDN Docs). If the number of clients was unknown I'd create a server that handled all the I/O from the clients, and route messages accordingly.
This would allow you to send messages to Clients that were offline and deliver them when they came online. Implement user authentication, and all manner of other goodies. Granted it may be serious overkill for what you want / need but a fun project all the same. I did mine in C++ and used TripleDES en/decryption for all I/O. I can't give it to since a Client paid for it and it effectivley belongs to them and I don't want to get sued.
You may even want to have a look and see if there's any free/shareware available before you start.
HTH
--
William
Software Engineer
ICQ No. 56047340