The the nav DVD is dual layer, should not be copy-protected, and is the same for Toyota and Lexus. The nav DVD in a Lexus vehicle should say Toyota on it actually. The only thing you cant do is mix different generations of nav DVDs.
My 2004 RX330 has a gen 2 while my sister's 2005 RX330 has a gen 3 so its not like we can both buy the latest update and make a copy on my PC with a dual layer burner (although for the sake of this forum I have to note that doing so would be illegal anyway...)
Hope this helps.