you can convert the the date that is posted by the datepicker to a timestamp using the strtotime() function.
in the insert record behavior, when you bind the date column to the date form element, it will generate code similar to:
[php]
<?php echo((isset($_POST["thedate"]))?$_POST["thedate"]:"") ?>[php]
change that to:
[php]
<?php echo((isset($_POST["thedate"]))?strtotime($_POST["thedate"]):"") ?>[php]
in order to store the timestamp.