That's where it pays off to be a computer engineer =). I think I'm going to go with an ITX board. I've seen examples in other cars that fit right into the dash. With a custom enclosure, I'm sure I could throw a touch screen on the outside and flush mount it.
As far as cost is concerned, it's either this or an in-dash DVD player for show. Suprisingly enough, their about the same price.
For anyone who's interested in the concepts behind it all,
http://www.mp3car.com has a nice faq on how it all works.