$result = db_query("SELECT n.nid FROM {node} n WHERE n.type = 'story'");
  
  while ($row = db_fetch_object($result)) {
   $node = node_load(array('nid' => $row->nid));
   foreach ($node->taxonomy as $tid => $tag) {
    if ($tag->vid == 3) {
     $node->taxonomy[$tid]->vid = 5; 
     $items[] = "updating tag $tag->name(tid: $tid) for $node->title";
    }
   }
   
   node_save($node);
  }
  
  $output .= theme('item_list', $items);

  print theme('page', $output);