아래의 스크립트를 페이지 상단에 놓고서 Input box에서 달력을 나타내게해서 날짜를 입력하는데요.
날짜 선택을 오늘이후부터 하도록 하고 3개월이나 4개월 이후는 날짜 선택이 안되도록 스크립트 수정을 하려고 합니다.  시작일과 종료일로 Input box 두개를 사용하려고 합니다.

고수님들 부탁드립니다..

------------------------ 스크립트 시작 -------------

<script type="text/javascript" language="javascript">
function positionInfo(object) {

  var p_elm = object;

  this.getElementLeft = getElementLeft;
  function getElementLeft() {
    var x = 0;
    var elm;
    if(typeof(p_elm) == "object"){
      elm = p_elm;
    } else {
      elm = document.getElementById(p_elm);
    }
    while (elm != null) {
      x+= elm.offsetLeft;
      elm = elm.offsetParent;
    }
    return parseInt(x);
  }

  this.getElementWidth = getElementWidth;
  function getElementWidth(){
    var elm;
    if(typeof(p_elm) == "object"){
      elm = p_elm;
    } else {
      elm = document.getElementById(p_elm);
    }
    return parseInt(elm.offsetWidth);
  }

  this.getElementRight = getElementRight;
  function getElementRight(){
    return getElementLeft(p_elm) + getElementWidth(p_elm);
  }

  this.getElementTop = getElementTop;
  function getElementTop() {
    var y = 0;
    var elm;
    if(typeof(p_elm) == "object"){
      elm = p_elm;
    } else {
      elm = document.getElementById(p_elm);
    }
    while (elm != null) {
      y+= elm.offsetTop;
      elm = elm.offsetParent;
    }
    return parseInt(y);
  }

  this.getElementHeight = getElementHeight;
  function getElementHeight(){
    var elm;
    if(typeof(p_elm) == "object"){
      elm = p_elm;
    } else {
      elm = document.getElementById(p_elm);
    }
    return parseInt(elm.offsetHeight);
  }

  this.getElementBottom = getElementBottom;
  function getElementBottom(){
    return getElementTop(p_elm) + getElementHeight(p_elm);
  }
}

function CalendarControl() {

  var calendarId = 'CalendarControl';
  var currentYear = 0;
  var currentMonth = 0;
  var currentDay = 0;

  var selectedYear = 0;
  var selectedMonth = 0;
  var selectedDay = 0;

  var months = ['1월','2월','3월','4월','5월','6월','7월','8월','9월','10월','11월','12월'];
  var dateField = null;

  function getProperty(p_property){
    var p_elm = calendarId;
    var elm = null;

    if(typeof(p_elm) == "object"){
      elm = p_elm;
    } else {
      elm = document.getElementById(p_elm);
    }
    if (elm != null){
      if(elm.style){
        elm = elm.style;
        if(elm[p_property]){
          return elm[p_property];
        } else {
          return null;
        }
      } else {
        return null;
      }
    }
  }

  function setElementProperty(p_property, p_value, p_elmId){
    var p_elm = p_elmId;
    var elm = null;

    if(typeof(p_elm) == "object"){
      elm = p_elm;
    } else {
      elm = document.getElementById(p_elm);
    }
    if((elm != null) && (elm.style != null)){
      elm = elm.style;
      elm[ p_property ] = p_value;
    }
  }

  function setProperty(p_property, p_value) {
    setElementProperty(p_property, p_value, calendarId);
  }

  function getDaysInMonth(year, month) {
    return [31,((!(year % 4 ) && ( (year % 100 ) || !( year % 400 ) ))?29:28),31,30,31,30,31,31,30,31,30,31][month-1];
  }

  function getDayOfWeek(year, month, day) {
    var date = new Date(year,month-1,day)
    return date.getDay();
  }

  this.clearDate = clearDate;
  function clearDate() {
    dateField.value = '';
    hide();
  }

  this.setDate = setDate;
  function setDate(year, month, day) {
    if (dateField) {
      if (month < 10) {month = "0" + month;}
      if (day < 10) {day = "0" + day;}

      var dateString = year+"/"+month+"/"+day;
      dateField.value = dateString;
      hide();
    }
    return;
  }

  this.changeMonth = changeMonth;
  function changeMonth(change) {
    currentMonth += change;
    currentDay = 0;
    if(currentMonth > 12) {
      currentMonth = 1;
      currentYear++;
    } else if(currentMonth < 1) {
      currentMonth = 12;
      currentYear--;
    }

    calendar = document.getElementById(calendarId);
    calendar.innerHTML = calendarDrawTable();
  }

  this.changeYear = changeYear;
  function changeYear(change) {
    currentYear += change;
    currentDay = 0;
    calendar = document.getElementById(calendarId);
    calendar.innerHTML = calendarDrawTable();
  }

  function getCurrentYear() {
    var year = new Date().getYear();
    if(year < 1900) year += 1900;
    return year;
  }

  function getCurrentMonth() {
    return new Date().getMonth() + 1;
  }

  function getCurrentDay() {
    return new Date().getDate();
  }

  function calendarDrawTable() {

    var dayOfMonth = 1;
    var validDay = 0;
    var startDayOfWeek = getDayOfWeek(currentYear, currentMonth, dayOfMonth);
    var daysInMonth = getDaysInMonth(currentYear, currentMonth);
    var css_class = null; //CSS class for each day

    var table = "<table cellspacing='0' cellpadding='0' border='0'>";
    table = table + "<tr class='header'>";
    table = table + "  <td colspan='2' class='previous'><a href='javascript:changeCalendarControlMonth(-1);'>&lt;</a></td>";
    table = table + "  <td colspan='3' class='title'>" + currentYear +"<br>" + months[currentMonth-1] + "</td>";
    table = table + "  <td colspan='2' class='next'><a href='javascript:changeCalendarControlMonth(1);'>&gt;</a></td>";
    table = table + "</tr>";
    table = table + "<tr><th>일</th><th>월</th><th>화</th><th>수</th><th>목</th><th>금</th><th>토</th></tr>";

    for(var week=0; week < 6; week++) {
      table = table + "<tr>";
      for(var dayOfWeek=0; dayOfWeek < 7; dayOfWeek++) {
        if(week == 0 && startDayOfWeek == dayOfWeek) {
          validDay = 1;
        } else if (validDay == 1 && dayOfMonth > daysInMonth) {
          validDay = 0;
        }

        if(validDay) {
          if (dayOfMonth == selectedDay && currentYear == selectedYear && currentMonth == selectedMonth) {
            css_class = 'current';
          } else if (dayOfWeek == 0 || dayOfWeek == 6) {
            css_class = 'weekend';
          } else {
            css_class = 'weekday';
          }

          table = table + "<td><a class='"+css_class+"' href=\"javascript:setCalendarControlDate("+currentYear+","+currentMonth+","+dayOfMonth+")\">"+dayOfMonth+"</a></td>";
          dayOfMonth++;
        } else {
          table = table + "<td class='empty'>&nbsp;</td>";
        }
      }
      table = table + "</tr>";
    }

    table = table + "<tr class='header'><th colspan='7' style='padding: 3px;'><a href='javascript:clearCalendarControl();'>Clear</a> | <a href='javascript:hideCalendarControl();'>Close</a></td></tr>";
    table = table + "</table>";

    return table;
  }

  this.show = show;
  function show(field) {

    // If the calendar is visible and associated with
    // this field do not do anything.
    if (dateField == field) {
      return;
    } else {
      dateField = field;
    }

    if(dateField) {
      try {
        var dateString = new String(dateField.value);
        var dateParts = dateString.split("/");

        selectedYear = parseInt(dateParts[0],10);
        selectedMonth = parseInt(dateParts[1],10);
        selectedDay = parseInt(dateParts[2],10);
      } catch(e) {}
    }

    if (!(selectedYear && selectedMonth && selectedDay)) {
      selectedMonth = getCurrentMonth();
      selectedDay = getCurrentDay();
      selectedYear = getCurrentYear();
    }

    currentMonth = selectedMonth;
    currentDay = selectedDay;
    currentYear = selectedYear;

    if(document.getElementById){

      calendar = document.getElementById(calendarId);
      calendar.innerHTML = calendarDrawTable(currentYear, currentMonth);

      setElementProperty('display', 'block', 'CalendarControlIFrame');
      setProperty('display', 'block');

      var fieldPos = new positionInfo(dateField);
      var calendarPos = new positionInfo(calendarId);

      var x = fieldPos.getElementLeft();
      var y = fieldPos.getElementBottom();

      setProperty('left', x + "px");
      setProperty('top', y + "px");
      setElementProperty('left', x + "px", 'CalendarControlIFrame');
      setElementProperty('top', y + "px", 'CalendarControlIFrame');
      setElementProperty('width', calendarPos.getElementWidth() + "px", 'CalendarControlIFrame');
      setElementProperty('height', calendarPos.getElementHeight() + "px", 'CalendarControlIFrame');
    }
  }

  this.hide = hide;
  function hide() {
    if(dateField) {
      setProperty('display', 'none');
      setElementProperty('display', 'none', 'CalendarControlIFrame');
      dateField = null;
    }
  }

  this.visible = visible;
  function visible() {
    return dateField
  }
}

var calendarControl = new CalendarControl();

function showCalendarControl(textField) {
  calendarControl.show(textField);
}

function clearCalendarControl() {
  calendarControl.clearDate();
}

function hideCalendarControl(flag) {
  if (calendarControl.visible()) {
    if (flag) {
      calendarControl.hide();
    } else {
      window.setTimeout('hideCalendarControl(true)',200);
    }
  }
}

function setCalendarControlDate(year, month, day) {
  calendarControl.setDate(day, month, year);
}

function changeCalendarControlYear(change) {
  calendarControl.changeYear(change);
}

function changeCalendarControlMonth(change) {
  calendarControl.changeMonth(change);
}

document.write("<iframe id='CalendarControlIFrame' src='javascript:false;' frameBorder='0' scrolling='no'></iframe>");
document.write("<div id='CalendarControl'></div>");
</script>


------------------------스크립트 끝 -----------

---------------------- --- Input 시작 (item.php)-----------

<INPUT maxLength="20" size="10" name="it_opt2" style="cursor:pointer" onfocus="showCalendarControl(this);" value="<?=$it[it_opt2]?>" itemname="종료일" required readonly>

------------------------------------------------