Thanks for all the replies guys,
1) this would be on my 92 300D 2.5, to be honest with you, unless I decide to get the engine rebuilt in the car, I will not install them, i do have emotional attachment to the car, but it is old and it has a lot of miles on it.
2) I have seen the aftermarket ones too, the monitors are under $200.00 each and the player is about $500.00, this also depends on brand and where you buy from of course. My friend has a car with a computer and MP3 player, internet access, wireless keyboard, etc. I think its pretty sweet for show. The internet connection is only 33.6 tops, and the monitors are pretty small, so its not the most practical thing, but its better than nothing i suppose.
The MP3 player will be most valuable to me I think, lol.
3) The monitors will fit in the headrests on my car, but you would have to cut out the material inside, etc. I guess you can tap into the power from the power seat motors/wiring.
4) as far as the emissions, unless you always leave them on, or have back passangers all the time, it shouldnt do any brain damage with it turned off <shrug>. I never really thought or researched about the health issue. Good point ymsin.