How to Create a Blank Page
I don't really advise this but here is a solution.

Create a php file in your Drupal root containing the following

&lt;?php 
define('DRUPAL_ROOT', getcwd());
require_once './includes/bootstrap.inc';
drupal_bootstrap(DRUPAL_BOOTSTRAP_FULL);
?&gt;


That will give you access to the full Drupal api. You can then put whatever markup you wish underneath.

A better method (but more complicated) would be just to create a custom page callback in a module then you can use that to either bypass Drupals theming, or you can make it change the theme to a custom one that produces very basic markup (you'd have to create that yourself).

If you want any details on how to do that let me know :)