i put an mp3 playing computer in my old buick a few years back

first off, i'm not to sure about about visual in a car so bear with me on this.

the video card i would recommend is "ATI: All in Wonder" the newer the better. also go with a soundblaster 128 or 512, unless you can get your hands on a 5.1 surround card (which reminds me!)

what head unit are you going to be using????

tell me more and i'll be glad to help you out.

also don't forget THE most important part of the system COOLING
i suggest keeping an open case in your trunk and using 4 or 5 cooling fans

also tell me more about that old computer