Show a PHP page in drupal 7
you should boot drupal on your file so that your file be aware of drupal functions,you can do this by :
YOUR_DRUPAL_ROOT= root of your drupal,here my drupal root was crawler.alexa.com. and 
require bootstrap.inc of your drupal.
and then boot drupal compeletly.
here is my example :

define('DRUPAL_ROOT', '../crawler.alexa.com');
require_once '../crawler.alexa.com/includes/bootstrap.inc';
drupal_bootstrap(DRUPAL_BOOTSTRAP_FULL);