When I tried to implement this solution, it did not work for me. So here is what I did.
<?php wp_list_pages('exclude=17,38&title_li=') ;?>
Copying and pasting this code as suggested only gets me a duplicate of my navigation menu. That sucks. But there's a better solution. The key is finding the code for the current navigation menu and adding the exclude code to that. Much cleaner and simpler, and no double nav bar.
Click on the presentation menu, go to theme editor and click on the header. Look for this code:
'sort_column=menu_order&depth=1&title_li='); ?>
This is the sort function and you can see that it is displaying the order, depth and title of each tab in the navigation. This is where we insert the exclude. For me, I wanted pages 16 and 17 excluded fromt the nav bar, so here's what mine looks like.
'sort_column=menu_order&exclude=16,17&depth=1&title_li='); ?>
Notice the addition &exclude=16,17 just substitute for the page numbers you want excluded.