if your stereo has a cassete player, then you could buy a cassette tape with a headphone jack built in. plug it in to your itouch, then put in teh cassette and it shouldplay.
YOu could see if you are has an auxillary port. Then get a auxillary cable (maybe 5-10$) and plug it in.
There are also these fm transmitters that you plug into your cigarette lighter, then attach your itouch to it via usb cable. It will broadcast a certain signal, and then you just go to your car radio and put it at the appropraite station.