The info that you are sending to Authorize.net comes from the confirm page. Until the confirm page is submitted done of the details are sent. Once the transaction is processed by Authorize.net the details are sent back to your site.
If you are looking to disable the form elements on the checkout form you could do so based on a session variable value. So on your confirm page you should have some session variables set for values from the form like the state. You can check on this session variable on the checkout form, if it has been set then disable the element. The code that does this might look like this:
<input type="text" id="text1" name="text1" <?php echo (isset($_SESSION['the state']) && $_SESSION['the state'] != "")?"disabled='disabled'":"" ?> />