I did a roof mounted install (so it can be seen from 3rd row) ... http://www.xoutpost.com/x5-e70-forum/...uk-photos.html

I took power from the centre console. The rear cigaratte lighter panel simply "pops off". I cut the cigarette lighter power cables, inserted a terminal/screw block and tapped off that for switched power - it comes on when the engine is started / 2nd stage of ignition (little hint, push the "start button" without your foot on the brake to boot up to 2nd stage ignition without starting the engine). My dvd player did not need a permanent power source - it stores all memory settings without it. Audio is via either InfraRed headphones (4 sets stored in the car), and I also have a cable which runs (hidden) to the aux-input, so you can listen to DVDs through the stereo.

Works great.