The basic connection requires 4 pins:
1 and 11 go to ground.
12 is TX and it goes to RX on Arduino, which is digital pin 0 on the Decimila Board.
13 is RX and it goes to TX on Arduino, which is digital pin 1 on the Decimila board.
You can read the full pinout at pinouts.ru.
This post is tagged ipod breakout board, pinout
Don’t you need to put a 500KOhm resistor between pin 21 and ground?
I saw that in other iPod references but found that it didn’t make a difference in my circuit. Please let me know if you have a different experience.