Use Carrier Pidgeons. Read the RFC for pidgeon packet protocols.
Ok.. sorry. You should be able to use a null modem cable to connect the computers together...not necessarily using the modems, but where they plug into. I don't know much able cables, but since it sounds like you don't have network jack/card on your laptop, or a nick in the computer--the only way is through the serial port... Can anyone else elaborate/correct?
Chalk