How do I find if a taxonomy term is used? I'm using drupal6 taxonomy.The content type 'B' is using a tag field which can use the title of the some of nodes of the content type 'A'.If any node of 'B' tagged a name or title of a node of content type 'A', I want to display one message in the respective node of 'A'.

Alternatively, is there any way to find if www.mysite/category/tag/term doesn't gives the "Page not found" error? This is to find if the term is used, or not.
If you have the term name, you can use the following code.

$nodes = array();

if ($term = taxonomy_get_term_by_name($term_name)) {
  $result = taxonomy_select_nodes(array($term-&gt;tid), 'or', 0, FALSE, 'n.sticky DESC, n.created DESC');
  while ($row = db_fetch_object($result)) {
    $nodes[] = $row-&gt;nid;
  }
}

if (!empty($nodes)) {
  // The taxonomy term is used from at least a node.
}