How to sort posts ascending in WP 2.5.1 ?

Hello,

in older versions of WP I can edit a file looking like this:
<?php
/* Short and sweet */
define(‘WP_USE_THEMES’, true);
$order=’ASC’;
require(‘./wp-blog-header.php’);
?>
The variable $order says how to sort.

What must I change in which file to see my posts sorted by date ascending ?

Thx for your reply.
Josef