disable textbox to enter values
===

I have textbox with datepicker. according to my requiremnt user must select either first tuesday or second tuesday of the month. So i disabled the rest of the dates using following code and its working fine.

    var dates_allowed = {
          '2012-07-24': 1,
          '2012-08-14': 1,
          '2012-08-21': 1,
          '2012-09-11': 1,
	  '2012-09-18': 1,
          '2012-10-09': 1,
          '2012-10-16': 1
    };
    $("#" + webinarDate.id).datepicker({
        // called for every date before it is displayed
        beforeShowDay: function(date) {

            // prepend values lower than 10 with 0
            function addZero(no) {
                if (no < 10){
                  return "0" + no;
                }  else {
                  return no; 
                }
            }

            var date_str = [
                addZero(date.getFullYear()),
                addZero(date.getMonth() + 1),
                addZero(date.getDate())      
            ].join('-');

            if (dates_allowed[date_str]) {
                return [true, 'good_date', 'This date is selectable'];
            } else {
                return [false, 'bad_date', 'This date is NOT selectable'];
            }
        }
    });


But problem is user can enter date in textbox instead of using datepicker(Which i dont want that). How to restrict the user to select date from datepicker instead entering manually. i hope you understand..