Well if you use a button, it is going to need java script to make it work and keep it pretty.
Here is what you might try: do a response.redirect back to the navigation frame, but use a query string to identify what page the user wanted to go to and then put that page in the other frame from the directory or just pass that query string over to the other frame and pull that data from the db. But it is going to cause the whole thing to refresh so it will not be as pretty as if you used a link. It is either doing it this way (to keep it more accessible) or you use java script which is terribly inaccessible. Keep in mind about 4% of the internet will not read your java script.