what i did with my factory radio, was when i got xm radio installed, i bought the audiovox xpress headunit, and it has a direct line in to the xm unit. if you go with the fm modulator, you get a pretty good and pretty clean, crisp sound. i know that getting xm may not be what you want to do, but it's another option (or an excuse to get it... haha). if you dont want to do that, go to crutchfield.com and do what michael said. however, if you do that, i believe you lose the ability to control the ipod through the ipod, it becomes all through the headunit. not 100% sure on that one though...