using smarty in modular web development

hi ,

i previously design and program a web site that have a index page that require various modules as needed via switch statement

assume that this is my index page so we have

<?php
require_once('includes/site.config.php');
//in config i have site wide setting , declaring objects , error handling , ....
require_once('includes/header.inc.php');
?>

<!-- content , tables , images , etc ... goes here -->

in main content center table i have this switch

switch($_GET["section"]){
case 'register':
require_once('modules/register.php');
break;
case 'about':
require_once('about.php');
break;
case 'users_list':
require_once('users_list.php');
break;
case 'news' :
require_once('modules/news.php');
break;
case 'site_policy':
require_once('site_policy.php');
break;
case 'contact':
require_once('modules/contact.php');
break;
default:
break;
}
<!-- after htmls include footer file -->
<?php include('includes/footer.inc.php');?>

now i learn smarty and i like to this web site have a template engine , the problem is i don't know how to assign this functionality to a tpl file plus in many place in the index page

i have to add another section and it's just possible with switch

for example : i have to require profile module and if this module called by user other modules like news , login, etc .. will be removed . so i use the following line of code :

if($_GET['section'] == 'profile'){
//do this and require news or login .etc .
}else{
require('path/to/profile.php');
}

an screen shot of site structure here

i think this task could be done like this

$smarty ->assign("section" , $_GET['section'] ) ;

//because the $_get super global return array

$smarty ->display("index.tpl");

then use {foreach } , {if} and {ifelse} statement to determaind switch

but i go thought many search but i can't find any professional programmer do such thing . so please let me know if there is a better solution to still writing entire web application

in one file and use smarty with it , without using switch to determine section to require modules .

Regards .

Mehdi .