Like nightingale2k1 said, you should be able to use that plug-in just fine with a FORM. Here's a quick example that uses a DIV instead:
<div id="pseudoForm">
<input type="text" name="first_name"/>
<input type="text" name="last_name"/>
</div>
<script type="text/javascript">
$("#pseudoForm").validate({
onfocusout:true,
rules:{
first_name:"required",
last_name:"required"
});
</script>
Notice how I used "onfocusout:true", which will make the plug-in validate when the user de-selects either element. You'll need to either use something like that, or else hook up your own event (probably in response to a button press) for the validation to be triggered, as the normal trigger (onSubmit) isn't applicable to DIVs.