I'm about to do that in my 16V! What I'm planning on doing is installing a PC in the car with a DVD-ROM and a TV-out video card. http://www.partsexpress.com
has really inexpensive LCD screens. They have 5.6" displays for only $160! I'll have a larger screen (maybe 6.8") upfront, then the 5.6" displays in the headrests.
For the PC, I'm still looking into DC-DC power supplies, which don't seem to be readily available, so I'll probably end up building my own. I have to put my electrical engineering classes to use somehow
Hope this gives you some ideas!