function navi(form) {
  var form_urls = [
    '4037324', // przetargi
    '4048919', // zamowienia UE
    '4100623', // komunikaty
    '4100637', // ruchomosci
    '4100641'  // nieruchomosci
  ]; 

  var w = form.announcementTypeAlias.selectedIndex;
  window.location.href = window.location.href.split('/').splice(0, 3).join('/') + '/komunikaty/0,79736,' + form_urls[w] + '.html';
}