BuddyPress.org

I have a working installation of WP2.9.1 with BP 1.1.3. I didn’t set it up myself and I actually don’t really understand how all the URL to display page mapping works. Now I want to add a new page that shows some static images (the same for all users). The page should look the same like the users starting page (URL /members/username), except that I want to show the images instead of messages. I know how to edit the theme so a new link is shown e. g. in the header or the user nav. But I couldn’t figure out where I have to create/edit/add something, so WP/BP knows what to do with an URL like “/members/username/static_images”. Could someone tell me, how this is done or at least where I have to start? I know PHP quite well (use it for approx 10 years), but I never had any contact with WP/BP before.