how to write a program to authenticate user on all availaible computers on a lan

hello
i want to write a program that can authenticate a user on all available computers on network
situation is this
when we type "\\<computer name>" on start menu run we are asked for a user name and a password upon giving information we are told that either authentication was suceesfull or un sucees full and we are authenticated on the computer.now i want to automate this process
can some one tell me what control,namepace and libray + protocol is used for this thing
because i think tcp or udp is not used for this and winsock will not work
i do nto want some one to feed me the code
i want some help is into what direction from where i should start

Try something with TCP ports 135 and 139. I don't know a thing about how it works, but those two are what my computer connects to when I go to \\beast in my home network.

To be more specific, the System process connects on 139 and Explorer connects on 135, so my guess would be authentication and the equivalent of keep-alive are handled by System, and browse requests are done by Explorer. Any more specifics than that, I have no idea.