Calling wp outside of the loop

Anyone know how to call WP code outside of the loop? For example, calling a wp-coded php file via ajax.

In the past, and up to 2.9.2, I believe, could use:

<?php
  // Include WordPress
  define('WP_USE_THEMES', false);
  require_once('PATHHERE/wp-blog-header.php');
  query_posts('showposts=1');
?>