do a web search for "hamachi". This is probably the most "user friendly" type of network when your mixing operating systems and dont know much about networking.
unless you dont have internet on the network... then hamachi wont work for you. If that is the case we would need to know what operating systems are invovled with the network, and if the network has any thing that is wireless, also what you are intending to use the network for? (game play? file sharing? rendering farm?)