hmm. sounds to me like a simple include, but that's probably inefficient.
[PHP]
<?php
$pages = "/path/to/pages/";
$default = 1;
if(is_file($pages.$_GET['id'].".php")) $p = $_GET['id'];
else $p = $default;
include $pages.$p.".php";
?>
[/PHP]
Just have all your pages as ID numbers.. IE: news page = 3.html
But that's really inefficient, and probably not how you do it =P