1 and try them, everybody is different, and likes different programs. There's MediaCar, FrodoPlayer, MediaEngine, etc. try 'em all, see for yourself which one you like best.
2 Do you mean a radar detector coupled with the computer? AFAIK nobody has done this yet,but it has been discussed before
3 A good Sat Nav for free? as in beer? I think warez discussion is forbidden on the forum, and there's no "good" navigation program that is free, there's some good comercial applications, but they are not free but go here you might be able to find something.