can´t get page title to work

Hello,

I installed the last stable version of page title module. The page title field appears appears also, when im editing a page, also I placed the code:

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

right after this line:
function _phptemplate_variables($hook, $vars = array()) {

What did I do wrong?

Thanks for any help,
Marc