It looks great except there is one thing missing...a navigation system.  I was considering retrofitting an OEM CTS navigation system but it would cost over $1500 at best to upgrade it myself.  I would need to buy the navigation unit, an antenna, the Bose amplifier, a new subwoofer, and all the extra wiring harnesses.  For a little over half of that cost, I could build a computer into the car that would be able to do much more than the factory navigation system.  The basic functions I wanted were media file playback (all audio and video formats), GPS navigation, DVD playback,  XM radio, and CD playback.  The finished product had a few bonus features including voice recognition, WiFi, Bluetooth, cellular data capabilities via a Bluetooth cellular phone acting as a modem, audio CD-ripping, automatic audio CD information download from CDDB, and CD burning capability.

There were a few constraints that I needed to keep in mind during the planning.  The factory LCD screen and radio circuit board needed to be preserved in order to still have control of the Driver Information Center (DIC).  I also wanted to keep OnStar functional and preserve the chimes that the car emits. 

I started preparing for the project by looking around for suitable computer parts.  I made templates of the parts out of cardboard to make sure everything would fit nicely.  The plan was to cut out the CD and cassette slot in order to mold a 7" touch screen into the dash.  All the computer parts would be able to fit inside the gutted case of the factory radio.

Proceed to hardware.