function datechange(grpName, formId, allowNulls) {
    var extraDayForNull = 0;
	
    if (allowNulls) extraDayForNull = 1;
	
    var xForm = document.getElementById(formId);
    var inpDay = xForm.elements[grpName + '_1'];
    var inpMth = xForm.elements[grpName + '_2'];
    var inpYr = xForm.elements[grpName + '_3'];
    var iCurrentDaySelected = inpDay.value;
    var iDayInMonth = DaysInMonth(inpMth.value - 1,inpYr.value) + extraDayForNull;
	
    var iCurrentDaysInMonth = inpDay.options.length + extraDayForNull;
	
    if (allowNulls) iCurrentDaysInMonth++;
	
    if (iCurrentDaysInMonth > iDayInMonth) {
	    inpDay.options.length = iDayInMonth;
	    if (iCurrentDaySelected > iDayInMonth) inpDay.selectedIndex = inpDay.options.length - 1;
    }
	
    while (iCurrentDaysInMonth < iDayInMonth) {
	    iCurrentDaysInMonth++;
	    inpDay.options[inpDay.options.length] = new Option(iCurrentDaysInMonth,iCurrentDaysInMonth);
    }
}

function DaysInMonth(xMon,xYear) {
    var firstofthisMonth = new Date();
    firstofthisMonth.setFullYear(xYear,xMon,32);
    firstofthisMonth.setMonth(firstofthisMonth.getMonth(),0);
    return firstofthisMonth.getDate();
}