What is it you want to see? TV or DVD?
I considered the BMW system but found it way to expensive. TV has to be a digital system anyway (DVB-T) in Holland.
I already had installed an Alpine system with screens in the headrests and a dvd changer.
I installed a DVB-T tuner and an override system for my navi screen. This works perfect ... also when you drive.
For dvd i would advise against a dvd changer (it is a waist of money). Freecom offers a very nice flat 100GB harddiskdrive with videou out for approx 150 euro. With Pocketdivx it means you can have up to 100 movies with you.
The only problem remaining: no aux-in for sound. I am hoping to solve this with the Dension Gateway 500 if it ever comes