Yes the truck is still driveable with the deck locked out. I did the same as you are considering doing. I bought our H3 with the 6CD changer, and then got a great deal on an OEM NAV unit from another member here. It came with t he head unit and CD, but no gps antenna. The head unit just plugs straight in to the existing harness, took about 15 minutes to install. The new antenna was about $35, and we mounted it on the roof for better reception. The deck would not work until it was unlocked by the dealer. As I was having a new security system installed, they didn't charge me to unlock it, but was told it would take about 1/2 to do. The OEM NAV unit is not as fancy by any means as the after market units, but integrates seamlessly with the truck (onstar etc.) and works pretty good. When I was looking, I found I wold have spent around minumum $1400 to get a new head unit, another $200 for mounting and interface crap, and then the hassle of plugging it all in. While it would have resulted in a fancier system with more features, it would have cost me 4x as much by the time I was done. I decided to go the OEM router and spend my pennies on other goodies.

 

I would still go aftermarket because of the additional features and the more sleek look. If you are worried about saving money buy a last year model and you will find double din units for $800 or less. I would rather get a unit that plays dvd's, wma files, mp3s, etc.

 

I need to talk to you more about that Tomm. The eBay deal fell thru.