Psuedo code

<?php

// set up the $module which defaults to 'index'
$module = isset($_GET['module']) ? $_GET['module'] : 'index';
$smarty->assign('mid_module',$module);

// include the "module" file, eg contacts, which contains the business logic
// eg databases queries.. and code to assign() the vars to $smarty
include("my_modules/$module.php");

// show the main smarty template
$smarty->display('page_container.tpl');
?>

// and the page_container.tpl
<body>

    <div id="content">
    {* the header block is included *}
    {include file='page_header.tpl'}
    
    {* include the module template *}
    {include file="$mid_module.tpl"}
    
    <!--- page footer-->
    </div>
</body>