I created a form using the Drupal forms API that contained a set of checkboxes. Here is the jQuery I added to validate the checkboxes and ensure at least one is checked before submitting the form.
<?php
$(document).ready(function(){
$('form#MYFORMID').submit(function(){
isChecked = false;
$('input[@type="checkbox"]', this).each(function(){
if ($(this).attr('checked')) isChecked = true;
});
if (isChecked) return true;
return false;
});
});
?>