Drupal on custom page? I created a .php page outside of Drupal. On that page I want to check if a user is logged into my Drupal site.

Is that possible?
If the PHP file is in the same directory where cron.php, and index.php files from Drupal installation are, then you can use the following code.

/**
 * Root directory of Drupal installation.
 */
define('DRUPAL_ROOT', getcwd());
include_once DRUPAL_ROOT . '/includes/bootstrap.inc';
drupal_bootstrap(DRUPAL_BOOTSTRAP_FULL); 

if (user_is_logged_in()) {
  //...
}


If the PHP file is in another directory, then you should use the following code.

/**
 * Root directory of Drupal installation.
 */
define('DRUPAL_ROOT', 'the directory containing the includes directory from Drupal');
include_once DRUPAL_ROOT . '/includes/bootstrap.inc';
drupal_bootstrap(DRUPAL_BOOTSTRAP_FULL); 

if (user_is_logged_in()) {
  //...
}