I know this is a noob question, but I can't find it anywhere.

Is there a way to make the Stock 03 Navigation accept inputs while you're driving? I wouldn't do it myself, but my passenger could.

 

Yes. Search around; you need to put an interrupt switch in-line with the vehicle speed sensor wire at the nav DVD unit. When you flip the switch, the unit will think the car is not moving, you can do whatever you want, then flip it back and it will update your position and get you back on track in a few seconds.