menu_tree.tpl is not called as per documentation

Hi there...

I'm trying to use Smarty with Drupal but I can't seem to get Smarty templates to get used. The documentation states:

Similar to PHPTemplate, it uses individual something.tpl (note extension is .tpl not .tpl.php) files to theme Drupal's theme_something() functions. Drupal's themeable functions are documented on the Development Plumbing site.

Does this apply to all themeable functions? My menu_tree.tpl is not being used when Smarty generates pages with menus -- at least as far as I can tell. Maybe I have something else wrong, but I'm not familiar enough with it to go about hacking up Smarty to debug it =).

Thanks!