There are some good bits and kits on
www.Mini-itx.com I've not dived in yet too many PC's / bits of PC's around the place at present.
WiFi between the car an home seems a must, as is a touch screen for display / control (expensive!) and a graceful start and shut down when the ignition is switched on / off. Delaying start up while cranking the engine and saving safely as you switch off.
Will you be blogging the project?