Edit in JSFiddle

var availableDates = ["15-1-2014","16-1-2014"];

$(function()
{
    $('#txtDate').datepicker({ beforeShowDay:
      function(dt)
      { 
        return [dt.getDay() == 0 || dt.getDay() == 6 || available(dt), "" ];
      }
   , changeMonth: true, changeYear: false});
});



function available(date) {
  dmy = date.getDate() + "-" + (date.getMonth()+1) + "-" + date.getFullYear();
  if ($.inArray(dmy, availableDates) != -1) {
    return true;
  } else {
    return false;
  }
}

<div class="clearfix">&nbsp;</div>
<h3>Custom Datepicker</h3>
<i>This date picker only allows users to pick weekends or the two dates specified in <code>availableDates</code></i>
<div class="clearfix">&nbsp;</div>
<input type='text' id='txtDate' />

              

External resources loaded into this fiddle: