WP menu for inner pages


I ma having a problem with getting a second custom menu to show on the interior pages

   This is in the header.php file in its original form
<div id="container"><!-- #container -->
        		<?php include_header(); ?>
        		<?php mainmenu(); ?>  

I want my interior pages to display a different menu I created e.g., interiormenu

I have tried using " if and else" statements and can’t get it to work.