In Car PC Theory
The Computer
Option 1: Run all of your cables to the trunk area and "dock" a laptop. You can take the laptop out when you're not driving or you can dedicate it to the car.
This is the option that i've been using for testing.
Option 2: Dedicate a PC to the car. Mini-ATX form factor seems to be the best, but more expensive. You can fit mini-atx just about anywhere.
With either option, you need some way of communicating with the computer. I have installed a touchscreen display which connects to the computer via USB. My GPS receiver also plugs into the computer via USB.
If somebody had an adapter to connect a pda keyboard to USB, that would rock. I used a permanent keyboard solution. The floppy rubber USB keyboard works fine. I kept playing with the idea of making it part of the sun visor.
The short answer:
The computer needs the following:
Power DC-DC PSU or Inverter
Input Device (touch screen and/or mouse/keyboard)
Monitor (LCD Display)
Audio output to Head Unit Aux input
GPS receiver (you want navigation right?)
Wireless Network Adapter (download new music/play games)
