This is what I have now. It sets the default correctly if I navigate to index.php.
PHP:<?php $page = preg_replace('/[\W\.-]/si', '', $_GET['page']); if (!isset($_GET['page'])) { $page = "home"; } include("include/$page.txt"); ?>
Added in the suggestion by philjohn but every page returned the 404.php as the include.
When you added his suggestion did you change the folder in his example "files" to "include"?