When I built a carputer I used windows XP and had it hibernate when the ignition was switched off. (Also allowed for quick booting) I had a 7 inch touchscreen to control it and used soem GPS software and a serial GPS receiver. All worked rather well
Played music, movies, DVDs, audio CDs.
However, I did write a custom app to do all the fancy stuff, never really finished, but it was in there and working. I have since sold the system to a mate of mine since I never really used it much beyone playing MP3s from a CD, so just got a cheap MP3 player in the car instead.
