Drupal 5.x

1) Where it says $vid=1;, replace the number 1 with the vocabulary ID number for the vocabulary you want to use to populate the drop-down with the terms in that vocabulary.

2) Where it says $formname="Company" (line 5);, replace the word Company with the word(s) you want your users to see as the default text in the drop-down after List by. Same changes in lines 2 and 4.

3) Optional: Where it says $options[] = t('List by ' . $formname);, replace List by with the word(s) you want at the beginning of the default text in the drop-down.

4) Where it says $options['http://www.example.com/taxonomy/term/'.$term->tid] = $term->name;, replace example.com with the URL of your drupal website, or, leave only '/taxonomy/term/' to user relative path.

$output = drupal_get_form('Company_dropdown_form', $form);
return $output;

function Company_dropdown_form() {
    $vid=1;
    $formname="Company";
   
    $vocabulary = db_query("SELECT td.name, td.tid FROM {term_data} td WHERE td.vid=%d ORDER BY td.name", $vid);
    // Initialise the country array
    $options[] = t('List by ' . $formname);
    //Populate array with url / name
    while ($term = db_fetch_object($vocabulary)) {
      $options['http://www.example.com/taxonomy/term/'.$term->tid] = $term->name;
    }
    //Build dropdown select
    //If we try to build OnChange directly it gets mangled, so put in array to confuse the forms api
    $form['category'] = array(
      '#type' => 'select',
      '#name' => $formname,
      '#id' => $formname,
      '#title' => '',
      '#default_value' => '',
      '#options' => $options,
      '#description' => '',
      '#multiple' => $multiple = FALSE,
      '#required' => $required = FALSE,
      '#attributes' => array('onChange' => "top.location.href=document.getElementById('$formname').options[document.getElementById('$formname').selectedIndex].value"),
    );
        return $form;
}

Drupal 4.7.x

Here is a working 4.7.x version of a Taxonomy Select Menu snippet that you can use for a block, on a page, or wherever you can put some PHP on your site. Only 4 or 5 things you need to change in the code below:

1) Where it says $vid=1;, replace the number 1 with the vocabulary ID number for the vocabulary you want to use to populate the drop-down with the terms in that vocabulary.

2) Where it says $formname="Company";, replace the word Company with the word(s) you want your users to see as the default text in the drop-down after List by.

3) Optional: Where it says $options[] = t('List by ' . $formname);, replace List by with the word(s) you want at the beginning of the default text in the drop-down.

4) Where it says $options['http://www.example.com/taxonomy/term/'.$term->tid] = $term->name;, replace example.com with the URL of your drupal website.

5) Where it says return drupal_get_form('company_dropdown', $form);, replace the word company with the same word you used in step 2) above - these two text strings must match.

$vid=1;
$formname="Company";

$vocabulary = db_query("SELECT td.name, td.tid FROM {term_data} td WHERE td.vid=%d ORDER BY td.name", $vid);
// Initialise the country array
$options[] = t('List by ' . $formname);
//Populate array with url / name
while ($term = db_fetch_object($vocabulary)) {
  $options['http://www.example.com/taxonomy/term/'.$term->tid] = $term->name;
}
//Build dropdown select
//If we try to build OnChange directly it gets mangled, so put in array to confuse the forms api
$form['category'] = array(
  '#type' => 'select',
  '#name' => $formname,
  '#id' => $formname,
  '#title' => '',
  '#default_value' => '',
  '#options' => $options,
  '#description' => '',
  '#multiple' => $multiple = FALSE,
  '#required' => $required = FALSE,
  '#attributes' => array('onChange' => "top.location.href=document.getElementById('$formname').options[document.getElementById('$formname').selectedIndex].value"),
);
//Output the form
return drupal_get_form('Company_dropdown', $form);

This is a result of the collaborative work on: http://drupal.org/node/48843 - you can see the development over there, and maybe get some questions answered. There is also a version that works with 4.6.x over there.

Extras

Ordering character variables like numeric ones
If you find that you have categories like 1, 10, 22, 2, 210 (extreme example) you can organize them as if they were numbers (i.e., a jump-menu like this: 1, 2, 10, 22, 210) rather than like text (i.e., a jump-menu like this: 1, 10, 2, 210, 22) by including the following in the jump-menu's SQL query:

db_query("SELECT td.name, td.tid FROM {term_data} td WHERE td.vid=%d ORDER BY LENGTH(td.name), td.name ASC", $vid);

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