The previous two posts are right! Heed their advice. I actually think the fm system is so dangerous that it should be banned, just like hands-on phones. You are constantly on the dial trying to find an open spot. Horrible. And the sound sucks as well.
Look at something like the Crutchfield site. There are many devices and even radios especially designed to work with iPods. Also, check into the TuneFlex.
You want to use the bottom port, not the headphone jack, with any installation. Finally, many auto companies offer factory parts to hook up iPods/phones.
I forgot: check out a local installer if you are confused. They probably have hooked up hundreds of people and know what works.