By default, Drupal will have only username and password for such a user. Whenever username is displayed, it will try to call a theme funtion namely username by specified $node. If you want to display user's fullname instead, you have to customize a little bit.

1. Enable profile module.
2. Add text field fullname.
3. Add phptemplate_username as follow to template.php.

function phptemplate_username($object) {
 
  if ($object->uid && $object->name) {
    // Shorten the name when it is too long or it will break many tables.
    if (drupal_strlen($object->name) > 20) {
      $name = drupal_substr($object->name, 0, 15) .'...';
    }
    else {
      $name = $object->name;
    }
    $profile = user_load(array('uid' => $object->uid));
    if ($profile->fullname) {
      if (drupal_strlen($profile->fullname) > 20) {
        $name = drupal_substr($profile->fullname, 0, 15) .'...';
      }
      else {
        $name = $profile->fullname;
      }
    }
 
    if (user_access('access user profiles')) {
      $output = l($name, 'user/'. $object->uid, array('title' => t('View user profile.')));
    }
    else {
      $output = check_plain($name);
    }
  }
  else if ($object->name) {
    // Sometimes modules display content composed by people who are
    // not registered members of the site (e.g. mailing list or news
    // aggregator modules). This clause enables modules to display
    // the true author of the content.
    if ($object->homepage) {
      $output = l($object->name, $object->homepage);
    }
    else {
      $output = check_plain($object->name);
    }
 
    $output .= ' ('. t('not verified') .')';
  }
  else {
    $output = variable_get('anonymous', t('Anonymous'));
  }
 
  return $output;
}

Tags: drupal