customizing check out process

[procella]

I am trying to make a two link form image.
I want it to both confirm the order and open a new custom size window at same time.
I belive the code for confirming checout is in tpl_checkout_confirmation_default.php something like this:

<?php
  echo zen_draw_form('checkout_confirmation', $form_action_url, 'post', 'id="checkout_confirmation" onsubmit="submitonce();"');

  if (is_array($payment_modules->modules)) {
    echo $payment_modules->process_button();
  }
?>
<div class="buttonRow forward"><?php echo zen_image_submit(BUTTON_IMAGE_CONFIRM_ORDER, BUTTON_CONFIRM_ORDER_ALT, 'name="btn_submit" id="btn_submit"') ;?></div>
</form></div>

Can I add here a tag like onclick="window.open('http://www.mywantedpage.com','newwin', 'toolbar,scrollbars,resizable,status,location,width=700,height=500,');?

or some php code that would do this aswell?

Sorry for my poor explanation.