Set the focus to the inputs and try tipping a date:

Date (original):
Date (modified):
Source code: 
<script type="text/javascript" src="jquery-1.4.2.min.js"></script>
<script type="text/javascript" src="jquery.maskedinput-1.2.2-co.min.js"></script>
<!-- source code version
<script type="text/javascript" src="jquery.maskedinput-1.2.2-co.js"></script>
-->

<input id="date0" type="text" size="10" maxlength="10" style="width: 80px;"/>
<input id="date1" type="text" size="10" maxlength="10" style="width: 80px;"/>

<script type="text/javascript">
jQuery(function($){
	$("#date0").mask("99/99/9999");
	$("#date1").mask("99/99/9999", {placeholder: 'dd/mm/yyyy'});
});
</script>