Page title module being ignored

I have the page title module installed, but the content I enter for each node's page title is being ignored. In Drupal 5.5, I apparently have to make a manual coding change in my theme's template.php file. When I do so, though, it breaks things. This is what the section of my current theme's template.php file has now:

function _phptemplate_variables($hook, $vars = array()) {
  switch ($hook) {
    case 'page':
      global $user;
      if ($vars['is_front']) {
        $vars['template_file'] = 'page-index';
      }
      break;
  }

  return $vars;
}

The module says to have this code:

function _phptemplate_variables($hook, $vars) {
  $vars = array();
  if ($hook == 'page') {

    // These are the only important lines
    if (module_exists('page_title')) {
      $vars['head_title'] = page_title_page_get_title();
    }

  }
  return $vars;
}

If I just replace the current code with the new code, it breaks things. I tried to merge the two, but it also breaks things. Can anyone help me figure out what the code should be with my theme? Thanks!