Start date: user can select start date as back as 6 months. example: if today is 04/23/2010 then i can go back up to 11/23/2009 but not more than 6 months.

<script type="text/javascript"> 
$(document).ready(function () { 

  $('#endDate').datepicker({ showOn: 'button', 
      buttonImage: '../images/Calendar.png', 
      buttonImageOnly: true, onSelect: function () { }, 
      onClose: function () { $(this).focus(); } 
    }); 


  $('#startDate').datepicker({ showOn: 'button', 
      buttonImage: '../images/Calendar.png', 
      buttonImageOnly: true, onSelect: 
        function (dateText, inst) { 
          $('#endDate').datepicker("option", 'minDate', new Date(dateText)); 
        } 
      , 
      onClose: function () { $(this).focus(); } 
    }); 


}); 

update code:

   var currentDate = new Date();
    var currentMonth = currentDate.getMonth() + 1;
    var sixMonths = currentMonth + 6 
    currentDate.setMonth(currentDate.currentMonth, sixMonths);
    var myNewCurrentDate = new Date(currentDate)
    $('#startDate').datepicker('option', { minDate: myNewCurrentDate });

i am getting currentDate = NaN