The standard 'out of the box' user registration form in Drupal is not the prettiest of forms and isn't very straight forward to theme either because it doesn't respond to simply creating a user--register.tpl.php in the templates folder. The old override method in Drupal 6 doesn't work anymore due to internal alterations that are way over my head. So I set about to find out how to theme a custom form I had built in Drupal 7.