You know... I think it would be useful if people assembled questions like yours and consolidated them in one area so that people could locate them...
Maybe some sort of cutsie acronym to remember easily, like FAQ.
Perhaps a handy link to the FAQ, maybe even in the navigation bar across the top of a set of forums. FAQ
To answer your question, you could get video to such a unit from a PC. Image quality will suffer and your touchscreen will only control the headunit functions unless you want to hack it yourself.
If you have serious interest in putting together a vehicle computer, I highly suggest doing lots of reading and reseach. It's not rocket science, but it does require planning and some thinking on your feet.
Welcome to the madness, compadre. Please check your sanity at the door.
Have you looked in the FAQ yet?
How about the Wiki?
Under normal circumstances, a signature would go here.