phptemplate themefunction

Hi all,

I'm trying to create a theme in phptemplate (I thought that was the best way to go, preparing myself for drupal 4.7).
The handbook tells me that if I want to change a standard theme function, I just follow the next steps:
* create a template.php
* find the function to edit
* put it in template.php
* replace theme_ with phptemplate_
* edit the function

But it won't work. I want to edit the breadcrumb trail.

This:

function phptemplate_breadcrumb($breadcrumb) {
  return '<div class="breadcrumb">Je bent nu hier: '. implode($breadcrumb, ' &raquo; ') .'</div>';
}

won't work.

Where am I going wrong?

Thanx in advance,

Evelien