Upgrading Garland-based theme from 5.x to 6.x

I've got a Garland-based theme, which works fine in Drupal 5.x, but I can't figure out how to get it to work under Drupal 6.x. When I say Garland-based, I took a copy of the files into a new sub-directory and modified node.tpl.php and template.php. The purpose was simply to allow me to format taxonomy terms differently.

I created a new function theme_terms(), added it to template.php and modified node.tpl.php to call it.

I changed node.tpl.php thus:

<?php if ($taxonomy): ?>
      on <?php print theme('terms', taxonomy_link('taxonomy terms', $node)) ?>
<?php endif; ?>

The function signature in template.php is:

function theme_terms($terms, $attributes = array('class' => 'terms')) {
  $output = '';
...
}

After upgrading my site to Drupal 6.x, I've got everything working except my mods to the Garland theme. I started with the D6 version of Garland, copied it and made the same changes as I did for D5, but no joy. I've read the upgrading guide and other D6 theme material. I've installed devel to assist, but no luck.

Can anyone explain what I need to do?