Using jquery form and validate plugins together

I'm new to jquery - I'm successfully using the jquery form plugin, but I want to be able to use jquery validate on the same form. How can I get it so that the form validates before submit?

Here's the jquery form code I'm using:

   
    $(document).ready(function() { 
  $('.sub_spinner').hide();
    var options = { 
        target:        '#output1',   // target element(s) to be updated with server response 
 beforeSubmit:  showRequest, // pre-submit callback       
 success:       showResponse  // post-submit callback 
    }; 
$('#myform').ajaxForm(options); 
}); 
function showRequest(formData, jqForm, options) { 
    var queryString = $.param(formData); 
  $('#test_null_submit').hide();
        $('.sub_spinner').show();
    return true; 
} 
function showResponse(responseText, statusText)  { 
       $('.sub_spinner').hide();
        $('#pfh').hide();
}

I've tried adding the script below before the above code, and what happens is it focusses on the field that doesn't validate, but submits the form at the same time.

   
      $(document).ready(function(){ $("#commentForm").validate(); });

And that's where I got stuck. Can anyone tell me how to combine the two so that it validates before it submits?

Many thanks