Question: will the screens be showing the same thing? If yes the setup is simple. Just buy a powered VGA splitter (if it isnt powered the quality will look bad). You can buy it from Provantage.com. The unit I bought is this one http://www.provantage.com/aluratek-avs04~7ALUT001.htm Its the smallest you can buy. Its about the size of a old school beeper. If you plan on running diffrent things, like I am doing (I have 5 screens in my setup), I think you will need more processor power if you plan on running video like I am. For music and GPS your setup will work. My setup uses heavy video. The first screen which is connected to the VGA port is strictly for the headunit screen that controls everything and displays GPS, engine diagnostic, and important stuff that the passengers dont care to see, this screen cannot see video and media stuff (I try to follow the law as much as possible). Screens 2,3 and 4 are connected to a powered VGA splitter then connect to the DVI port on my PC. These screens show all multimedia stuff. Screen 5 is strictly for rear monitoring. Originally I bought a 1.5 ghz VIA M10000 board, but it could not handle video at all. So I went ballistic and bought a 1.8 dual core AMD turion, a Kino-690s1 Mobo, and 2 gigs of ram. This system is over kill, but I wont have any doubts of it doing what I want it to do.
When it comes to GPS I guess it depends on preference. I went with a bluetooth cigarette lighter unit, but I have to assume most people go USB because you dont have to worry about the pairing mess. I just didnt want the PC to have to power it, and I didnt want to worry about batteries.