I finally managed to connect my iPod to my car's audio system, using Dension ICELink. My car has an Audi Symphony II with a built-in 6-CD-changer, and no support for direct line-in -- apparently, it will only accept audio signals on the line-in port if an external CD changer signals its presence on the car's internal bus. That's what the ICElink does.
Sound quality is excellent, I can step through songs with the control keys in the radio, integration with the GPS system and the cell phone support is supposed to work as well (haven't tried that yet) - all in all, pretty neat.
2005 UPDATE:
After reading your post I purchased the IceLink adapter. I really wanted it to work just like yours, but the new IceLink’s lock the iPod’s controls and display and force you to use special playlists and the radio buttons for “safty” reasons.
With a little more reasearch and talking to Dension (who was hard to get a hold of) I found out there is a website http://www.mp3yourcar.com/ where they have adapters that allow full control and display on the iPod still… lower price too.
John Gavin