first, i wouldn't really worry about the sound card of the laptop, if that's the only thing putting you off, then don't even worry about that. it's minor, you won't notice a difference if your head unit's going to rendering the sound.
otherwise, it's very possible to mount a computer in the car. i know a few people who have (or have tried
) doing it. you could put the case under the seat, with the front facing the drivers side (so loading CDs, etc. wouldn't be too hard). you can buy a small screen at any car audio place (if you really want to buy one though, send me a PM, i'll get you a good deal). and all screens have inputs that you can use from pracitcally anything, be it a playstation, computer, etc. the only limit is your imagination. so now that that's set up, you could invest in a good touch screen
(talking expensive), or if you're really 1337, you could fabricate a mount for a trackball mouse on the right of your seat
so when you want to change songs, all you do is just put your hand on the mouse, and move through the list
there's really many, many ways to do it. i've seen, and helped friends install, dozens of these setups, whether for playing music, or for gaming. as far as power supplies go, don't worry about that. that's the least of your worries.
however, if you could tell me what car it's going to be for, and if you know what alternator you have at the moment that would be great
