www.newegg.com has Shuttle pc systems for under $500. You need an inverter to go from 12V to 110V AC dependent on what power source you are using in the car. You want to get a high wattage inverter because of the loads the pc will take. Other than that just split the input onto the navi screen, I don't know what kind of input connectors it has. My suggestion would be to do research on the navi screen and see what all it has electronics wise and then get the appropriate components.