Another ancient project, I constructed a small PC to use as a music player in my truck. In the first incarnation the system consisted of a Mini ITX motherboard and case with a power supply that accepts 12 VDC input power and an Emerson 5 inch LCD TV and separate track pad for the UI.

The PC was stuffed under the driver's seat and wired into the audio system while the TV display was mounted just below the dashboard where it was visible to the driver and passenger. The trackpad was loose and could be hand held or rest on the bench seat. This was not an optimal method for user input but it worked.

This was not the intended application of this hardware, at the time in car computer entertainment systems were not common yet. So it did require some hacking. I.E the TV power button had to be modified to automatically turn on when the TV received power.
The operating system was Red Hat Linux 7.3 with a full gnome desktop install and XMMS as the music player with the Blursk visualization plugin to make the UI a little more fun. The open source Trident drivers included with Red Hat Linux did not support the TV Out option so a custom driver from the motherboard supplier was required to enable the use of the TV for a display.

The music media consisted of Ogg Vorbis encoded files ripped from a large collection of Compact Discs. In the end there were a few hundred CDs worth of music available at the touch of a button versus the more common 6 disk CD players that were often installed in the trunk.
At one point the guys over at Mini-Box.com provided a new case they were developing for use in compact installations. The case was very small, included a key pad on the face as well as a small LED character display. The new case required a laptop hard drive to replace the 3.5" drive from the original OggBox, but the reduction in size was significant.