I have seen many people ask how to get news, weather, video, iPod music, google maps, and how about ANYTHING that runs on your iPhone to display on your in-car Nav screen.

In-Car Video Screen (I have the MyGig)
NAV-TV with AV input Harness (Or Lockpick I guess)

Apple AV Output Cable
ScreenSplitr (Jailbreak your iPhone, search Cydia - TVOut gives Better video FPS but NO Landscape mode)

With your iPhone plugged into your Nav Screen using AV cables (I'll do a full write-up later), run ScreenSplitr. Thats all...
You will see your iPhone Screen Mirrored on your Screen. Any application you run on the iPhone will display on the myGIG screen. Imagine the possibilities... Pandora, Google Maps, Red Light Cameras (Atoll.CoPilot is cool), SlingPlayer (Watch live TV on your MyGIG Screen). The only Issue I have with screensplitr is frame-rate. It does compress the video output and freame-rate is not the greatest due to the mirroring on the iPhone 3G, but it works and looks good enough for now!

Here is my short video! [ame=http://www.youtube.com/watch?v=TUvmgqlg2tY]YouTube - iPhone Screen to MyGIG[/ame]