Programmatically select primary menu item

Hi,

I've got a 2 level primary menu navigation system

Eg.

- Fashion
- Products
- Brands
- News
- Lifestyle
- Products
- Brands
- News

Each node has already been tagged to a 2nd level item (i.e. Fashion -> Product). Ideally, when you view the node itself, the menu item Fashion -> Products should be set active. But its not doing that.

I know there is a module called menutrails that would help. But my server resources is at its max and I don't want to install anymore modules.

So the only way I can think of is either add a php snippet on the node template itself, or use the template.php file to intercept the menu_local_tasks and force it to add an "active" class to the menu item thats programmed

So far I only found this resource http://drupal.org/node/195198 that shows what I want.. but its for Drupal 5.x

Does anyone know how to do it for Drupal 6.x?