how can i get Drupal webform confirmation message on popup?
Here is an example using a custom module (called it wcm_overlayer). Basically, this will show the confirmation message in an overlayer using the jQuery Fancybox library. For the webform configuration (under form settings), you need to set the redirection location setting to No redirect (reload current page).

wcm_overlayer.module

/**
 * Implements hook_init()
 */
function wcm_overlayer_init()
{
    // Add library &amp; js file
    drupal_add_library('wcm_overlayer', 'fancybox');
    drupal_add_js(
        drupal_get_path('module', 'wcm_overlayer') . '/js/wcm_overlayer.js');
}

/**
 * Implements hook_node_view()
 * 
 * @param type $node
 * @param type $view_mode
 * @return boolean
 */
function wcm_overlayer_node_view($node, $view_mode)
{
    // Verify if webform is attached to a node
    if (!isset($node-&gt;webform)) {
        return false;
    }

    // Retrieve confirmation message
    $confirmation_message = check_markup(
        $node-&gt;webform['confirmation'], $node-&gt;webform['confirmation_format']);

    // Retrieve all status message
    $messages = drupal_get_messages('status');

    // None is found, don't do anything
    if (!isset($messages['status'])) {
        return false;
    }

    // Loop through all messages and get confirmation message
    foreach ($messages['status'] as $message) {
        if ($message !== $confirmation_message) {
            drupal_set_message($message);
            continue;
        }

        $found = true;
    }

    // Confirmation message is not found, don't do anything
    if (!isset($found)) {
        return false;
    }

    // Confirmation message is found, pass this as a setting
    drupal_add_js(array(
        'wcm_overlayer' =&gt; $confirmation_message,
    ), 'setting');
}

/**
 * Implements hook_library()
 * 
 * Define the jQuery Fancybox 1.3.4 as a library
 * @return string
 */
function wcm_overlayer_library()
{
    $path = drupal_get_path('module', 'wcm_overlayer');

    $libraries['fancybox'] = array(
        'title' =&gt; 'jQuery Fancybox',
        'version' =&gt; '1.3.4',
        'js' =&gt; array(
            $path . '/js/vendor/jquery.easing.js' =&gt; array(),
            $path . '/js/vendor/jquery.mousewheel.js' =&gt; array(),
            $path . '/js/vendor/jquery.fancybox.js' =&gt; array(),
        ),
        'css' =&gt; array(
            $path . '/css/vendor/jquery.fancybox.css' =&gt; array(),
        ),
    );

    return $libraries;
}


js/wcm_overlayer.js

(function ($) {
    Drupal.behaviors.wcm_overlayer = {
        attach: function(context, settings) {
            if (!settings.hasOwnProperty('wcm_overlayer')) {
                return false;
            }

            this.showOverlayer(settings.wcm_overlayer);
        },
        showOverlayer: function(message) {
            $(window).load(function() {
                $.fancybox({ content: function() {
                        return $(message);
                }});
            });
        }
    };
}) (jQuery);


Hope it helps.