Hi there! I also have an 03 and I installed the Pioneer AVIC-Z2 (
http://www.pioneerelectronics.com/PU...ection=models).
I have the adapter to allow me to control it (most of the functions) from the steering wheel, as well as the Sirius adapter, OnStar adapter, iPod adapter, and rear color camera. I also have the Bluetooth adapter but have not had much luck with it.
You can read more about the Pioneer's here:
http://www.avic411.com/forum/
Be sure to check out the "Z" forums.
Good luck and lemme know if you have nay questions.
-Matt