Zooming interface linking inquiry

I’m hoping someone can help. The file below (d-load the zipped up version below) uses various movieclips which are then placed on the screen into z-index levels. So the user can use their mouse and zoom in and out. You can navigate to certain levels by clicking a button within that level. BUT…and here is my question:

How can I create buttons that always stay on the top and don’t move that will navigate to certain levels. So you could have five buttons on top…and clicking one would zoom you to a certain level… does that make sense?

Check out the file below and see what you think.

http://www.secrettechnology.com/screens/flashtunnel.zip

thanks heaps!