Wanting to install Nav system

Im wantint to install a aftermarket navigation system in my car to replace the factory radio thats in the car right now, but I got a question before I actually do this. As you all should know, the factory radio allows you to changs some settings, and also reset your tire monitoring system if needed. How would I be able to do these things if I remove the factory radio?
This is what I was looking at
http://www.crutchfield.com/S-W3Z7LBnHR4t/cgi-bin/ProdView.asp?g=182350&I=113DNX7100

My car also has onstar, and i also wanna know if that will be affected...
2002 Impala LS

not sure about onstar, I know it ties into a lot of the electronics in the car. If it ties into the radio, it'll have to stay in the car no matter what but the radio can be relocated and still work.

If the features ur talking about is in the factory radio, I can remove all the necessary electronics from the radio and build a custom panel for ur HUD and mount it somewhere else out the way of the nav system

not sure about onstar, I know it ties into a lot of the electronics in the car. If it ties into the radio, it'll have to stay in the car no matter what but the radio can be relocated and still work.

If the features ur talking about is in the factory radio, I can remove all the necessary electronics from the radio and build a custom panel for ur HUD and mount it somewhere else out the way of the nav system

Well, I called one of the service advisors at the dealer, and he said that it is possible to add a diffrent unit, but somehow I gotta keep that factory unit connected at the same time. So, I just spent the last 45 mins searching for this wiring harness that I dont even think exists, but I did manage to find the harness to retain my door chimes, and onstar. And yes, I did stupidly spend the $215 to have my onstar upgraded so it would work in 2008:banghead:. I dont even care about the steering wheel controls working or not... Do you guys think this is one of those things that should be put on the "forget it" pile? Because this thing is starting to give me a headache, and I havent even started yet!

All the features that the radio controls are also manually controllable. For example, resetting the tire monitor is something like turning the headlights on and off 3 times in a row. Resetting the oil life system is flooring the gas 3 times in a row with the engine off, but the key to on. Everything has a manual control somewhere and is described in the manual. THis way, you don't need to relocate the factory radio. As for onstar, I believe PAC audio has an interface to put it up to a new radio.

I was about to post a new thread on this topic, so I'd like to ask about this too. I want to upgrade to a new radio and was wondering if I'll lose any functions at all with a non factory radio. Will my compass, trip navigator work the same? Will I still get the Low Tire Pressure warning? Other than needing to reset these things manually, will anything be different than right now with the factory radio installed? What about the anti-theft that's built in?

I have a 2003 Impala LS. The factory radio is a CD/cassette.