I don't know much about the BIPES. My car has the 6 disc changer + BOSE and I can use the iPod in that car with the little FM transmitter thing if I want. For the $18 spent, it's worth every penny cuz it keeps the kids quiet - - it's a beatiful thing
Here's one very similar to what I got:
Griffin Technology: iTrip Auto Universal Plus
They have much fancier units costing up to $80. I selected something simple, and without a rechargable battery, so I could evaluate the overall performance without getting in too deep.
I think they've got units that are powered by the iPod itself, but that's gonna have a dramatic impact on battery life.