I recently needed to add functionality to the Password Policy module so I thought I would outline the steps I took in a blog post. The Password Policy module is used to enforce a stricter password policy on users on a Drupal site. This means that when a user creates or changes their password they must conform to certain rules like the password length, or if it contains upper and lower case characters. There are a set of rules to chose from and they can be fully customised by the site administrators. It's a good module, you should check it out.