For the sake of those who haven't read the original post, I'm copying it here with some modifications for the pre-2005 RX:
Press the MENU button, then press the DVD button (however the car must be stopped before the DVD button is available). Then touch the TOP LEFT of the screen, then the BOTTOM LEFT of the screen, then the TOP LEFT again, then the BOTTOM LEFT again, then finally touch the BOTTOM RIGHT of the screen. It will bring up the SYSTEM MENU. Press and hold the OVERRIDE button for about 3 seconds until it turns green, then hit BACK. If you do this while moving, you won't be able to edit until you stop the first time. If you are stopped when you do this, then you can continue to edit while moving.
You MUST do this everytime you start your car.