First, what ever you want to buy at circuit city WILL NOT work PERIOD.
Since you already look at mp3car store, get the screen/monitor from there.
But I would suggest you to hold off your purchase and research.
Read this thread New to CarPCs? Don't know where to start?
and Show off your project and search for Dodge Neon. I am sure there are more than 1 dodge neon install available or maybe other similar dodge/chrysler available.
Also read the FAQ Emplorium.