I started a thread on this a while back. From what I can tell (and I am not a technician) if you have the 2006 with the Leather/Sunroof package, you should already have most of the sensors (round thing on the top of dash, center by the window).
From looking at the parts and service manual. I "think" you only need the following:
Control, Auto Temp Control - [HAF] Fahrenheight - 55111010AD
Module, Power Blower Motor - [HAF] - 4885482AC
I suspect you will also need the starscan to activate and calibrate the system. The parts are somewhere around $200 new. I never got around to actually trying this though.
I am still interested if this actually works, but just have not had the time to play, and access to the starscan will be difficult as the few inquiries I made to the dealership on if this was possible turned out to be dead ends. They apparently do not like when we tinker with our vehicles.