function SearchPage() {

   var categorie = document.getElementById('dropdown_search');
   var searchTerm = encodeURIComponent(document.getElementById('main_search').value);
   var catvalue = categorie.getAttribute('value');

   if (catvalue != null) {
         catvalue = '&value=' + catvalue;
   }
   else {
      catvalue = '';
   }
   location.href = 'default.aspx?cmd=result&searchtext=' + searchTerm + catvalue;
}