If you hit the Menu button you should see Map DVD on top right of screen. Press that button. It will give you the version of the Map DVD you are currently using. However, if it has been changed, it will not be the one that came with the car. I believe the 2006 is a gen 5 system.
BTW, I just replaced the 4.1 to 7.1 disk DVD in my 2005 RX330.
The steps are easy. THe NAV DVD us under the jack tray at the rear of the car. There are two plastic round head pop in bolts (one on the left, one on the right) that pop our when pried with a screwdriver. The Nav unit is on the right under the tray. Put the key and turn to acc postion. There is a slider on the front of the unit (it faces the driver door) on the top left of the unit as you are facing it. Slide it the other way (I think it was to the left.) The disk will eject in a couple of seconds. Put the new disk in and push the slider back to the origional postion. Replace the two plastic pins and you are all set.
