Name anchoring for WordPress Menus

I’ve been going at this for a while without much luck. Could anyone explain how I would rewrite this code so that the effect of scrolling down a single page is still the the same, but instead of automatically listing pages from the site I’d be able to generate custom menus from WordPress’s built in menu tool? Thanks.

<ul id="mainNav">
       		<li id="nav-home"><a href="#home">Home</a></li>
			<?php
                $pages = get_pages('sort_column=menu_order');
                foreach ($pages as $page) {
                $link = '<li id="nav-'.$page->post_name.'"><a href="#'.$page->post_name.'">'.$page->post_title.'</a></li>';
                echo $link;
                }
            ?>
    	</ul>