Ive got a full prepared a working HTPC type system going into my road car it based around the itx platform due to its low power consumption and heat. I use the Voom PC case which is powered off a modified vehicle PSU I run this through a touchscreen which supports the input and visual side of things.. the rest of the parts are generic pc parts such as hard disk, optical drive etc.

My system has motion sensor detection which turns on recording cameras and uploads the images via the wireless internet connection to the server in my home to be reviewed at a later date. It also has a GPS reciever which allows the use of a wide range of navigation systems.
The wireless and pcmcia slot means I always have internet access should I be near a insecure Wi-Fi network or by using my Vodaphone Datacard.
The hard disk contains the media (music and film) because disks can skip and obviously also the computers operating system.

Im currently trying to workout how to use the boot password of the computer to product the ignition system also for added security but not yet achieved this