If you just want to start small and connect a wired laptop, then a simple ethernet cross-over cable along with static IP address(es) will do the job.

I normally just keep handy a 10cm length of cat5 with RJ45 plugs on each end, wired as a cross-over cable. This is used in combination with a double-ended RJ45 jack coupler, similar to the one embedded inside the docks I made/make.

CrazyMelki has a wireless router in his car, and syncs music from his apartment to the car over that link. Perhaps he'll tell us how it's all powered -- probably just a DC/AC inversion gizmo -- not the most efficient (power), but pretty simple to hook up.

Cheers