The cars with preinstalled TVs in the dashboards turn the screen off when you engage gear. Don't know about the new generation of self fit DVD players, but would count them as potentially lethal if there's no failsafe.
no doubt any distraction in a car while you are driving is potentially lethal.
what i'm really after is the music storage side of things. i have a ridiculous amount of CD's in my car. i wanted to store them and play them via my laptop.
of course my laptop would have the added facilty of having a display that could in theory act as a DVD screen (for when i am stationary of course), an interface between car and me that gives me real time diagnostics of the cars performance and a large screen sat nav system.