Try setting startDate to startDate:"<?php echo date('d/m/y'); ?>" inside your JavaScript, using PHP to obtain the current date, e.g.

if( jQuery.datepicker ){
    jQuery(".cf_date").datepicker({startDate:"<?php echo date('d/m/y'); ?>", buttonImage: "js/calendar.gif", buttonImageOnly: true, dateFormat: "mm/dd/yy" });
} else {