Get the PIE adapter, they are cheap on ebay... around 60 bucks shipped. Install them into your mustang cd radio.

 

Belkin makes a darned good FM Transmitter. I used my friends Belkin on the way to Phoenix and only had trouble with it once.
Or you could just buy a new deck that has either an Ipod input or a USB drive input, hell even a AUX in will work for Ipods.

 

i recently installed the PIE adapter... best thing ever... you can listen to your ipod with your stock system and i have mine hidden safely away in my center console.. you can get all the cables from crutchfeild.