Originally Posted by k0nr4d

If you ujst want to block the html page, then you could do
<?php
$array[] = 'http://www.site1.com';
$array[] = 'http://www.site2.com';
if(!in_array($_SERVER[HTTP_REFERER],$array)) { exit(); }
?>

This could of course but done more compactly code-wise but that should get you started.