Get the CCK field value using dbquery
Here is a little example, how to make requests in Drupal 6. You may change table name and field name and it should work for you.

$query = db_query('SELECT n.nid, regid.regid_FIELD_VALUE
   FROM {node} AS n
   JOIN {regid_FEILD_TABLE_NAME} AS regid ON regid.vid = n.vid 
   WHERE n.type = %s AND n.status = %d, $your_node_type, 1);

$result = array();
while($node_data = db_fetch_object($query)) {
  $result[] = array(
    'nid' =&gt; $node_data-&gt;nid,
    'regid' =&gt; $node_data-&gt;regid_FIELD_VALUE,
  );
}