I am extremely surprised the insurance company can force you to have it installed at a certain store. I know in Canada, you can take it anywhere you feel like. Same with repairs to the car. You can get serveral quotes, but by no means are you required to take it to the lowest priced, or the one the insurance company prefers.
Well, here's the deal. The insurance company has a contract with Circuit City to do inspections on audio/video equipment in the cars they cover. The installation was actually supposed to come out of my pocket. They are sending me an AVIC-D3 from my request. But my original AVIC-N1 that was damaged retails for much higher than the D3. The company doesn't send cash for you to purchase a new Navi. So because of the price difference between the two, they will be sending me a voucher for use at Circuit City for free installation, and an extended warranty. (my policy for customization in my car only covers up to $1500 and they don't value the AVIC-N1 at $2000 anymore). Hope that clears it up.