The datepicker widget has a min and max date attribute.
<script>
$(function () {
$("#datepicker").click(function(){
$.datepicker.setDefaults($.datepicker.regional["es"]);
$("#datepicker").datepicker({
dateFormat: 'yy-mm-dd',
firstDay: 1,
minDate: new Date( *enter your start date here* ),
maxDate: new Date( *enter your end date here* )
});
});
});
</script>
Documentation: http://api.jqueryui.com/datepicker/