Thanks. But I managed it myself.
Solution is :
<html>
<head>
<title></title>
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.6/jquery.min.js" type="text/javascript"></script>
<script src="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8/jquery-ui.min.js" type="text/javascript"></script>
<link href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8/themes/base/jquery-ui.css" rel="Stylesheet" type="text/css" />
<script type="text/javascript">
$(document).ready(function() {
$("#txtFromDate").datepicker({
onSelect: function(selected) {
var date = $(this).datepicker('getDate');
if ($('select').val() == '1') {
date.setDate(date.getDate() + 6); // Add 7 days
} else {
date.setDate(date.getDate() + 13); // Add 7 days
}
$("#txtToDate").datepicker("option", "minDate", selected);
$("#txtToDate").datepicker("option", "maxDate", date);
$('#txtToDate').val('');
}
});
$("#txtToDate").datepicker();
$('select').change(function() {
$('#txtToDate , #txtFromDate').val('');
})
});
</script>
</head>
<body>
<form id="form1">
<select>
<option value="1">Weekly</option>
<option value="2">Fornightly</option>
</select>
<input type="textbox" id="txtFromDate" />
<br/>
<br/>
<input type="textbox" id="txtToDate" />
</form>
</body>
</html>
