From a glance at your site, it looks like you may have already figured this out, but just in case - to edit your page template go to header.php in the theme folder and put this function under the < h1 > displaying the title:
<?php wp_list_pages(); ?>
You can then wrap that function in a div and style the list to appear horizontally.
Alternate solution:
I haven't tried this, but there is a plugin for creating menus in WordPress - here's a link:
http://wordpress.org/extend/plugins/allwebmenus-wordpress-menu-plugin/
Or just search for 'menu' in http://wordpress.org/extend/plugins/