How to game on a network


My network is up and running fine say i 

wanted to play Desent on the computer in the next room how do i join the game on the other
computer? Do i use lan to lan? or Ipx or what? The TCP is used over the internet only 1 computer is on line.All i want to do is play head to head with my son raceing and fighting of course.any help is nice go into
detail i’m thick headed. Thanks