Prova così
Codice PHP:
<select name="regioni" id="regioni" onChange="loadList('province', getSelected(this)); loadList('comuni', getSelected(document.getElementById('provincie')));" 
                          </
select></td
                        </
tr
                        <
tr
                          <
td><label for="regioni">Provincia</label></td
                          <
td><select name="province" id="province" onChange="loadList('comuni', getSelected(this));"
                            </
select>                          </td
                        </
tr
                        <
tr
                          <
td><label for="regioni">Comune</label></td
                          <
td><select name="comuni" id="comuni"
                            </
select