I've looked at this idea a number of times and have come to the conclusion that the best solutions are either handheld (Garmin, Navman etc) or PC based (using the Earthmate).

Xenarc do a great 7" touchscreen that would make the ideal interface for a PC based in car solution. And cheap laptops with USB are more than enough for these sort of requirements.

 

ALPINE navigation, (if you can get the acura DVD thats the best one) is the greatest. Well worth the money.