replacing stock stereo, non-working navi

I'm planning in changing the stock stereo with an alpine system, while trying to get info at crutchfield.com they state that if you replace the stock stereo the navigation system will not work, is this true? how is this conected and how can it be avoided, that's $2000 to be wasted.

i dont know the ans. but try calling your local nissan dealer ship or parts and sevice dept.