use magento default datepicker plugin in your project

<action

method="additem"><type>js_css</type><name>calendar/calendar-win2k-1.css</name><params/><!--<if/><condition>can_load_calendar_js</condition>--></action>

method="additem"><type>js</type><name>calendar/calendar.js</name><!--<params/><if/><condition>can_load_calendar_js</condition>--></action>

method="additem"><type>js</type><name>calendar/lang/calendar-en.js</name><!--<params/><if/><condition>can_load_calendar_js</condition>--></action>

method="additem"><type>js</type><name>calendar/calendar-setup.js</name><!--<params/><if/><condition>can_load_calendar_js</condition>--></action>

<block type="core/html_calendar" name="head.calendar" as="calendar"

template="catalog/html/js/calendar.phtml"></block>

</reference>

var valid_date =

calendar.setup({

    inputfield :

‘valid_date‘,

    ifformat : ‘%y-%m-%d‘,

button : ‘date_from_trig‘,

    singleclick :

true

});