function setDays() {
  var y = document.registration.StartYear.options[document.registration.StartYear.selectedIndex].value;
  var m = document.registration.StartMonth.selectedIndex;
  var d;
  if ( (m == 3) || (m == 5) || (m == 8) || (m == 10) ) {
    days = 30;
  }
  else if (m == 1) {

    if ( (Math.floor(y/4) == (y/4)) && ((Math.floor(y/100) != (y/100)) || (Math.floor(y/400) == (y/400))) )
      days = 29
    else
      days = 28
  }
  else {
    days = 31;
  }
  if (days > document.registration.StartDay.length) {
    for (i = document.registration.StartDay.length; i < days; i++) {
      document.registration.StartDay.length = days;
      document.registration.StartDay.options[i].text = i + 1;
      document.registration.StartDay.options[i].value = i + 1;
    }
  }
  if (days < document.registration.StartDay.length) {
    document.registration.StartDay.length = days;
    if (document.registration.StartDay.selectedIndex == -1) 
      document.registration.StartDay.selectedIndex = days - 1;
  }
}