There are a few different ways to connect a ipod to a car. list below:
1:FM transmitters (worst cause of quality lost) these are crap but they are the easiest and cheapest
2:cassette adapter (better still some quality lost)
3:ipod to car kit (its hardwired to factory stereo) (best) no quality lost, pretty much perfect cd quality sound in less you have some interference ,it also charges your ipod too (quiet expensive and hard to hook up) currently I have one but I do have the new ipod touch and it doesnt work with it.......
4:aftermarket stereo with aux out put (best) no quality lost, perfect cd sound, easier to install but of course you need to buy a aftermarket deck with aux outs.
if you have any more questions ask away. ive done these all.