Most iPod adapters use the CD changer input in your car stereo head unit, so you could disconnect the changer and connect an adapter. Unfortunately, these adapters usually translate playlists as CDs, meaning you can cycle through six playlists but can't navigate the entire player. You can also get hard-wired FM modulaters that connect directly to the FM antenna input. Harmon Kardon makes a very good system, called the Drive + Play that offers full control of the iPod and can hook into the antenna input or use the CD changer input. And if you have an iPod hooked up to your head unit, you really don't need the CD changer.
OK, I was all set to buy a Peripheral PXDP Ipod2Car iPod Car Adapter, but the tech geeks at Crutchfield.com told me it is not compatible with my Ford Escape 2003 with a 6-CD changer. I don't want to buy an itrip or any other FM transmitter. What are my hard-wired options?