WordPress.org

Installing la petite url is a breeze.

1. Upload the le-petite-url folder to the /wp-content/plugins/ directory
2. Activate the plugin through the 'Plugins' menu in WordPress
3. Place <?php the_petite_url_link(); ?> in your template where you'd like the shortened URL link to show up.
4. If you'd like to use a separate domain for your shortened links, see this article.