I've tried this on a 2004 Camry with navi and the screen does exist, haven't got around to testing it while the vehicle is in motion. A member over at toyota-4runner.org confirmed that it works on 2004 Solara and 2005 4Runner. I believe it should work with all Toyota navis since they all appear to the be same head unit. My wish was that since Toyota incorporates a passenger seat occupied sensor that activates and deactivates the passenger airbag, they should allow inputs if a passenger is present. This trick works, but it's just an extra time the engine is started.
It's pretty easy to do, Menu>Volume, touch the speaker icon (top left), lower left corner, speaker icon, lower left and release your finger. Basically, top left corner, lower left corner, top left corner and lower left corner in the Volume settings screen. It'll take you to a service screen, hold down the override option until a beep is heard. That will override the speed sensor and allow inputs for the navi.
Here's the link to the 4Runner forum:
http://www.toyota-4runner.org/showth...threadid=11889
Here's the link to ClubLexus where the service menu was originally discovered:
http://www.clublexus.com/forums/show...2&postcount=10
Hope this helps Toyota owners with navi out when they have a passenger who wants to input destinations. Drivers, please your eyes on the road.