What I advise you to do is to call or email guys at LogJam Electronics - they are pretty helpful with the stuff - they sell interfaces and cables for car audio etc. I just bought SNHOND3 interface from them and I was told that they have miniplug adapters etc. Their site is www.logjamelectronics.com - check it out and give'em a buzz.

I used it to hook up my Sony CD-mp3 changer as a Direct Connect audio option (controlled from stock stereo) but you can use it for any AUX input - only difference is that of course you will have to operate your audio software on the laptop by yourself (and if you ask me that's kind of a drag when you are going 80 mph on a highway).

Good luck!