Just added Zen Lightbox to my cart based on Cherry Zen Template. Had to make a couple of template alterations to get the drop shaddow back to normal. so thought I would post my file here for others to use if needed.

( sorry if its been done before )

File is the tpl_modules_main_product_image.php in your templates folder.


PHP Code:
<?php
/**
 * Module Template
 *
 * @package templateSystem
 * @copyright Copyright 2003-2005 Zen Cart Development Team
 * @copyright Portions Copyright 2003 osCommerce
 * @license http://www.zen-cart.com/license/2_0.txt GNU Public License V2.0
 * @version $Id: tpl_modules_main_product_image.php 3208 2006-03-19 16:48:57Z birdbrain $
 * modded to include Zen Lightbox v1.4 aclarke 2007-09-15 for the Cherry Zen Template by Jettrue
 */
?>
<?php 
require(DIR_WS_MODULES zen_get_module_directory(FILENAME_MAIN_PRODUCT_IMAGE)); ?> 
<div id="productImage" class="centeredContent back">
<!-- bof Zen Lightbox v1.4 aclarke 2007-09-15 -->
<?php

if ($current_page_base == 'product_reviews') {

$zen_lightbox_products_name $products_name_reviews_page;

} else {

$zen_lightbox_products_name $products_name;

}

if (
ZEN_LIGHTBOX_STATUS == 'true') {

echo 
'<script language="javascript" type="text/javascript"><!--
document.write(\'<div id="productMainImage"><a href="' 
zen_lightbox($products_image_largeaddslashes($products_name), LARGE_IMAGE_WIDTHLARGE_IMAGE_HEIGHT) . '" rel="lightbox[gallery]" title="' addslashes($zen_lightbox_products_name) . '">' zen_image($products_image_mediumaddslashes($products_name), MEDIUM_IMAGE_WIDTHMEDIUM_IMAGE_HEIGHT) . '</div><br class="clearBoth" /><span class="imgLink">' TEXT_CLICK_TO_ENLARGE '</span></a>\')//--></script>';

} else {

echo 
'<script language="javascript" type="text/javascript"><!--
document.write(\'<a href="javascript:popupWindow(\\\'' 
zen_href_link(FILENAME_POPUP_IMAGE'pID=' $_GET['products_id']) . '\\\')">' zen_image($products_image_mediumaddslashes($products_name), MEDIUM_IMAGE_WIDTHMEDIUM_IMAGE_HEIGHT) . '<br /><span class="imgLink">' TEXT_CLICK_TO_ENLARGE '</span></a>\')//--></script>';

}

?>
<!-- eof Zen Lightbox v1.4 aclarke 2007-09-15 -->
<noscript>
<?php
  
echo '<a href="' zen_href_link(FILENAME_POPUP_IMAGE'pID=' $_GET['products_id']) . '" target="_blank">' zen_image($products_image_medium$products_nameMEDIUM_IMAGE_WIDTHMEDIUM_IMAGE_HEIGHT) . '<br /><span class="imgLink">' TEXT_CLICK_TO_ENLARGE '</span></a>';
?>
</noscript>
</div>