Adding a special layout to a catagory

I was wondering about something. On my website, I would like to have a special layout once people enter the Private area (registered users only). For this layout, I would prefer to have other header.php and footer.php files than for the main layout. Now, I would like it that, whatever theme my visitors are using, they always get to see the same layout when they go to the private area. How should I do that? Is this possible, is there a plugin? How? Any help would be gradly appreciated.