wrap edit pages_menu.tpl as follows... (4.0.5 code)
Code:
{* $Id: pages_menu.tpl,v 1.4 2004/06/24 09:53:29 max Exp $ *}
{section name=pg loop=$pages_menu}
{if $pages_menu[pg].pageid ne "5"}
{$pages_menu[pg].title}
{/if}
{/section}
then add your link to page 5 where ever you need to