For a true bare bones computer system, check out the VoomPC, by VIA and Min-box. It's actually made for your a car or other vehicles and goes for $299-$399. Integrating the Mini-box M1-ATX 12V power supply unit, it can protect itslef from power surges and eliminate car battery drain by monitoring battery levels, even when the car isn't running. Hoping to allow car manufacturers to add things like GPS navigation, communication, entertainment and information functionality (perfect for law enforcement, rescue and commercial transport), the computer's processor is VIA's C3 1000MHz chip. Also gives six-channel surround sound. Comes with USB2.0, Firewire, Ethernet, PCMCIA types I and II CardBus interface for GPRS/Wifi, S-Video and VGA.
VIA and Mini-box Announce the VoomPC [Mobilemag]