My brother just bought the new Lexus IS350. He too as an aux jack in his car and also wanted to connect an ipod (ipod nano). It was very easy to do and all you need is a audio cable. The audio cable you need has two 3.5mm plugs on both ends. You connect one end into the ipod and the other end into the aux jack. Play something on your ipod and put your speaker system's input on aux. This is what we did on his car and most likely will be the same for yours.
Best,
Ken