What's the point in 2Gb of Ram and 3Ghz dual-core processor outputting to a 7" screen in a loud rattly vehicle? all it'll lead to is mega stress in case it gets stolen, more headaches as you try and get it all configured without overheating in a contained rugged vibrating harsh environment, and the increased fuel cost of making your alternator crank up a 320W PSU on top of all your car's vital electrical systems.
Unless you're building a show car with six plasma TVs and NASA shuttle communication capabilities, scale your system back about seven billion percent. You'll be thankful for the simplicity when it inevitably goes wrong.
If you still want power, but minus the desktop setup, then go with mobile components. Yea its more pricey, but you wont have to worry about powering it. A OPUS 320 will work fine. I built my setup for high multimedia use. 4 screens, etc.....
Nirwana Project, the Android/Win 7 hybrid system!
1X Ainol Novo Flame Tab
3x Perixx Touchpads
3x 7 inch Screens
1X 7 inch motorized Screen
1x Win 7 PC