The easiest way and cheapest is to go with an rf module. Very easy to use.
Plug in I Pod to unit (through headphone jack) plug other end into ciggarette lighter.
Tune to unused station, usually 89.5 or some crap like that.
Done, that simple even for you. You will lose reception now and then, but it is the cheapest way.
Here is one of those cheap ones, they also have more expensive ones, depends on your wallet.
http://www.scosche.com/products/sfID1/210/sfID2/322/productID/418