i have a dedicated computer in my car, the way i get sound to the system is through the aux input in my deck, check to see if u have one, if not u can use a wired FM Modulator, i dont recommend using a wireless method, it will do but the sound quality will be horrible, the best way is to tap into the aux if u have one.
In my old stanza I made an mp3 player out of a chopped down computer. It was running a 333 celeron processor and 256 megs of ram. The most expensive part in the entire thing was the video card (voodoo 2, 32 megs), which I picked up at a used parts store for like 35 bucks. The entire thing was mounted in my glove box, and the display it used was a 6.5 in lcd module.
You'd be suprized what you can do with computer tech. My friend Walt helped me rig up win98 so that it only boots the necessary software, and winamp 2.
Oh, and for the topic (sorry, strayed a bit), I got an old audio card from the same parts store, which actually had rca outputs, so I was able to run it right into the back of the head unit.
You could try running it this way. Go to Radioshack and pick up both an rca signal booster, and a headphone to rca converter cable. Plug the headphone to rca converter into the laptop's audio out, and then plug the rca into the signal booster. I believe this thing is designed to run off a house source power, so you might want to pick up a power inverter as well. The RCA booster will make the sound quality crisper and clearer than without it.