With this code you can:
-- Add two taxonomy comboboxes from diferent parents.
-- Add a combo box with the title of a list of nodes

The Objective:

Create an efect like this:
http://jquery.geronimo.com.ve/

To search with 3 criterias autofilling the combos

        //First Combo
        $vector2 = taxonomy_get_children(152, $vid, 'tid');
        $output .= "<form name='SEARCHFORM' method='post' action=''><select id='child152' name='child152'>";
        foreach($vector2 as $c=>$v)
            $output .= "<option value='".$c."'>".$v->name."</option>";
            $output .= "</select>";
        //Second Combo
        $vector3 = taxonomy_get_children(153, $vid, 'tid');
        $output2 .= "<select id='child153' name='child153'>";
        foreach($vector3 as $c=>$v)
            $output2 .= "<option value='".$c."'>".$v->name."</option>";
            $output2 .= "</select>";
        //Third Combo
        $taxo_id = 6;
        $list_no = 10;
        $term1 = 'CLUTCHES' ;
        $term2 = 'G.M / CHEVROLET' ;
        $term3 = 'G.M / CHEVROLET' ;
        $term_count = 2;
        $sql = "SELECT n.title , n.nid from {node} n INNER JOIN {term_node} tn ON n.nid = tn.nid INNER JOIN {term_data} d ON d.tid = tn.tid WHERE d.name IN('$term1','$term2') GROUP BY n.title HAVING COUNT(*) = $term_count";
        $output3 .= "
	        <select id='tit_combo' name='tit_combo'>
        ";
        $result = db_query($sql);
        while ($anode = db_fetch_object($result)) {
        $output3 .= "<option value='".$anode->nid."'>".$anode->title."</option>";
        };
        $output3 .= "</select>";
        $bothcombos=$output."</br>".$output2."</br>".$output3."<br/> Hola Mundo";
        return $bothcombos;