Success! I was able to figure out how to write the most basic netcode, and get four to five divers surfing around on LAN. I think this is a pretty good base to start on - once the Jam officially starts, I'll work on the actual game-play.
Technical details: The client side communications are implemented using SFML's socket library. The server, on the other had, is written in python using Twisted. Each client opens up a TCP and UDP channel - a randomly generated id associates the two channels together. This is also the id that's displayed above each divers head.