Duffin,
It is really easy. To remove the nav screen, check this article:
http://www.xoutpost.com/articles/all-...n-removal.html
Basically while the nav monitor is in the 'up' or 'open for cassette' position, you can pop off the frame. Once that is removed you will see 4 torx screws that need to come out then the whole unit easily comes out of the dash. That's it. Once you are back there you will find a loose cable for the aux input connection or it may be bundled up with another harness but it is not hard to find.
Any questions let me know.