When going to drupal 6 I needed also to upgrade our theme.
I had everything quiet fast, just the menu-tree was a big pain.
The code for the drupal 5 theme was:
print theme('menu_tree',variable_get('menu_primary_menu',0));
And now for drupal 6 it is:
print menu_tree($menu_name = 'primary-links');
menutree.module?
Just curious... why not just use: http://drupal.org/project/menutree ?
Depencency
I just don't think that a theme should have a dependency.
Finally
Thanks DenRaf. I spent hours on Drupal searching for this and all of the snippets I was finding were for Drupal 5. Finally, I've got a drop down menu working with Drupal 6 Primary Links. :)