Hi Robert,
No offense intended but it is both not possible and a really bad idea :-D
Not all asp.net controls work inside updatepanel, ones that don't include menu and treeview.
Even if they did work, making your entire navigation based on updatepanel ajax postbacks would be very inefficient, prone to viewstate errors and viewstate bloat, would create a lot of problems if the user uses the browser back button, users won't be able to bookmark your pages, it would be horrible for SEO. Those are just a few issues that come to mind immediately.
I would ask why do you want to do this, what are you trying to accomplish by this approach?
Best,
Joe