Newbie question: adding nav receiver to Prius II

I'm by no means versed any much car anything. However, I have tinkered with computers and other electronics, so I'm not completely in the dark about what I'm asking.

Is there a starter guide to replacing the Prius II's stock stereo with a navigation system? I know it's possible, but I want to be sure to retain all the non-radio functionality, steering wheel controls and probably other things that I'm forgetting about.

Also, in regards to satellite radio... I have a separate kit since I use it at home and in the car. I know the Prius is wired for XM, is there any chance when I do the stereo install that I'll be able to connect the antenna to my car dock?

Thanks!!