I still can’t get X to run over that port, and I haven’t even tried to encode off the cable yet.
Overall, I’m fairly pleased with my progress so far.
I also solved my wireless problems and my lack-of-PCI-slots problems in one fell swoop.
I removed the wireless card, and ran 100 feet of cat5 cable along the baseboard. I now have 100BASE-T switched ethernet in my living room. I am the man!