Creating a new custom page (or tpl.php ?)

Hi,

I am trying to implement a new page (custom_page.php) into my drupal design. All the other pages feed off the page.tpl.php and link appropriately but I wish to have a page going to (custom_page.php).

This works fine, within the menu system I am capable of linking to this individual file. My concern is that I tried using the primary navigation supplied by drupal within the (custom_page.php) and it did not pick up;-

<?php if ($primary_links): ?>
<div id="main-nav">
<?php print theme('links', $primary_links); ?>
</div><!-- /primary_menu -->
<?php endif; ?>

I copied pretty much the same code from (page.tpl.php) header and pasted it within my new page but it was not being seen, can anyone suggest advice?

Thanks.