The only way to add navigation is through an aftermarket unit. The OEM version requires new cables and amplifier... CD changer optional.
The aftermarket choices are fixed or portable. Alpine, Eclipse, Kenwood and Pioneer all make a fixed mount unit that goes in the dash. Otherwise you can pick up a portable unit that mounts to the windshield.
←
You could put a 04 nav in, And the rear camera. You can watch movies while driving. The 05 nav doesn't even play movies at all, So the 04 has the most to offer seen as LEXUS went backwards with the 05 nav. Interested? I also have 05 nav if that is what you want.