The main thing to remember when disconnecting the nav computer is NEVER remove the connections if there are any blinking lights on the face of the nav drive. Always make sure the unit is inactive before removing power.
Your preferences will not be lost if you remove it.
You didn't mention the year of your X5, but assuming it has the widescreen monitor then here are instructions for how to remove that -
http://www.xoutpost.com/articles/all...n-removal.html