ok - I think you need to use something like this:
<!--YOUR SITE CONTENTS HERE-->
<?php
$number = 5;
if(!empty($_GET(id)))
include("news/show_news.php");
else
include($_GET(id));
?>
<!--END OF SITE CONTENTS-->
You are using a URL variable to pass the page id. So when you are using base it just pulls the index.php?do=whatever.php
Which I take it is failing?
Also if you use the code above - you could use a case statement to handle what pages to include and handle any situations when the user has entered their own id=pagename.php