Custom Theme Support

Hi guys,

Ive just set up a WordPress site with a custom (downloaded) theme, the theme itself says that it supports one custom menu, however i am able to create more custom menus.

The thing i cant seem to figure out is how to show the custom menu i have created. Ive been looking at the code to register the custom menu but im not really sure on what it should be.

here is the original portion of the code that registers the menu:

function inkthemes_register_custom_menu() {
    register_nav_menu('custom_menu', __('Main Menu', 'themia'));
}

add_action('after_setup_theme', 'inkthemes_register_custom_menu');

function inkthemes_nav() {
    if (function_exists('wp_nav_menu'))
        wp_nav_menu(array('theme_location' => 'custom_menu', 'container_id' => 'menu', 'menu_class' => 'ddsmoothmenu', 'fallback_cb' => 'inkthemes_nav_fallback'));
    else
        inkthemes_nav_fallback();
}

function inkthemes_nav_fallback() {
    ?>
    <div id="menu">
        <ul class="ddsmoothmenu">
            <?php
            wp_list_pages('title_li=&show_home=1&sort_column=menu_order');
            ?>
        </ul>
    </div>
    <?php
}

Then in the header is:
<?php inkthemes_nav(); ?>

Could anyone possibly show me how i would get this to register and show a second custom menu (the second menu is created in wordpress admin area and is called Shop Menu)

Thanks.