The same as you play any game LAN. Have two or more computers, each of which with the game installed, you must use seperate copies of the game, because if the game is installed with the same serial key it will recognise it and block access. Make sure both are hooked up to the same network, then enter the multiplayer LAN menu, you should see the other player in the lobby once both of you are in there. One person then creates a game, which will appear on the others screen. Enter the game set the options and play.