Just recently installed the Xbox for my son to use on long trips, he really likes it. Most games look great on the screen... games with small images are difficult to see, my kids don't care.. they have Xbox in the car!!!
I used a 300 watt power inverter to power the Xbox, I mounted the game console behind the 3rd row seats, used the 12 volt accessory plug on the left side of 3rd row seats to power the inverter.
One problem I ran into was having a long enough cord for the Xbox audio and video connections to reach the a/v plug in for the DVD system. I purchased a 10 ft a/v cord with male and female ends. The female end plugs into the existing Xbox cord and the male end plugs into the a/v plug in for the DVD.
Becuse my son has an Xbox and a PS2, I opted just to bring in what he wants on a trip. I already have an inverter from 4 years ago and I just place the console on the floor...those things heat up pretty well that I don't want to warp my leather seats.
One thing about the 7" screen, my son seems to be staring up at it. No complaints from him but I found fully reclining the seat makes him look a bit more comfortable in my eyes.