if you want to use the ipod an rf modulator will work well. another, better solution is to use and Ice-Link. Dension produces them, and they integrate the ipod with a stock or aftermarket head unit. it actually allows you to control the ipod's functions through the head unit and even steering wheel remotes. it is only available for specific car models and aftermarket units, so check the website if what you have is compatible.
http://www.dension.com