Make sure to setup an ip-adress for your network card (not your internet ip).
It should be something like this:
X is a different number on each computer.
Then just start the game on every computer, let 1 computer make a multipayer game (not through the internet) and the other computers should be able to join your game.
And ofcourse, first make sure the computers can find eachother under windows, if they can't the problem lies somewhere else.