I didn't have nav in my 02 sl, but in my 01 Lexus the nav dvd was in a seperate player from the cd changer. Disk 1 in the cd changer played dvds on the nav screen provided the emergency brake was pulled up. Took about 10 seconds to override that. I can watch movies and still have the nav system working.

We just bought an '05 E320 with the AMG sport package and love it. The dealer never told us anything about this. The navigation works really well.