Can't import audio "undefined function" error

When I try to import audio, I get this error:

Fatal error: Call to undefined function: taxonomy_form_alter() in /home/chucklin/public_html/sites/all/modules/audio/contrib/import/audio_import.pages.inc on line 39

Here's the relevant section of audio_import.pages (// $Id: audio_import.pages.inc,v 1.2 2008/09/30 04:43:07 drewish Exp $):

if ($files) {
    if (module_exists('taxonomy')) {
      // here's a little hack to get the taxonomy controls onto our form
      $form['type'] = array('#type' => 'value', '#value' => $form['#node_type']);
      $form['#node'] = new stdClass();
      $form['#node']->type = $form['#node_type'];
      taxonomy_form_alter($form, array(), $form['#node_type'] .'_node_form');
      unset($form['type']);
      unset($form['#node']);
    }

Anybody know what's going on? Seems like the taxonomy module messes everything up in Drupal 6, but I need it.