function validate_required(field, alerttxt) {
  with (field) {
    if (value==null||value=="") {
      alert(alerttxt);return false;
    } else {
      return true
    }
  }
}

function validate_form(thisform) {
  with (thisform) {
    if (validate_required(expression,"Please enter a search term")==false) {
      expression.focus();
      return false;
    }
  }
}