Drupal 6: Export all fields and their content types to CSV

gistfile1.php

<?php

$content_types = node_get_types();
$header = array(
  'Source content type',
  'Source content type machine name',
  'Source field name',
  'Source field machine name',
);
$sql_field_type_collector = "
  SELECT `field_name`, `label`
  FROM `content_node_field_instance` nfi
  WHERE nfi.`type_name` = '%s'
";

$rows = array();
foreach (array_keys($content_types) as $type) {
  $rows[] = array(
    $content_types[$type]->name,
    $type,
    '---',
    '---',
  );
  $sql_field_type_collector_result = db_query($sql_field_type_collector, $type);
  while ($field = db_fetch_array($sql_field_type_collector_result)) {
    $field_info = content_fields($field['field_name'], $type);
    $rows[] = array(
      $content_types[$type]->name,
      $type,
      $field_info['widget']['label'],
      $field['field_name'],
    );
  }
}

$out_file = 'fields.csv';
$fp = fopen($out_file, 'w');
fputcsv($fp, $header);
foreach ($rows as $row) {
  fputcsv($fp, $row);
}
fclose($fp);

This looks like exactly what I'm looking for, but how do I actually use this code? Do I just pop it in the template.php?

@JacobDB, instead of putting it in template.php, I recommend using Devel module. You can use adhoc PHP at URL path /devel/php. Another alternative is to run this by Drush's php-script command.
Hope this helps.