I've downloaded the .zip jscalendar file from this issue's thread: http://drupal.org/node/81691
I then followed the instructions as for how to add the jscalendar to the form (by adding the jscalendar to the form's attributes, as a class).
The icon is there, next to my date textfield, but clicking on it just submits the form, as if I pressed the preview button, and it does nothing more than that...

here's the code I'm using:

<?php
$form['field_expiration_date'][0]['value']['#attributes'] = array('class' => 'jscalendar');
?>