Networks

Hi, I am doing a project, in it 16 computers connenct to a electronic cicuit and then they build a network by that, but the info I need is this:
1: What should my circuit send and recieve if I want to connect my computer by using Windows XP's cross network cable(COM)(I want the circuit to play the role of the server computer in that)
2: How long are the packets in this kind of network and how should I distinguish the target IP of each packet and how long it is?