After much waiting and such like, here, finally, are my settings to get the SpaceNavigator working within SL.
Firstly, we have the settings for the RBC9 driver. As you can see I've just mapped the SpaceNavigator axis almost randomly ;) Just make sure you map to the joystick axis of X,Y,Z, and rX, rY and rZ.
Secondly, we have the settings from within Second Life itself. The 'Joystick Flycam' is found within the 'Client' menu (CTRL+ALT+D to turn it on, if you haven't got it).
Here are my settings:
