Here it is:

$header_template = 'tpl_header.php';
$footer_template = 'tpl_footer.php';
$left_column_file = 'column_left.php';
$right_column_file = 'column_right.php';
$body_id = ($this_is_home_page) ? 'indexHome' : str_replace('_', '', $_GET['main_page']);
?>
<!-- BOF SMART BACKGROUNDS -->
<?php //Smart Backgrounds
$smart_image = '';
if ($current_page_base == 'index' or $current_page_base == 'product_info') { //add _ and cPath to bg filename only if individual cat bg image exists, else add _ and top cat id to bg filename only if top cat bg image exists
$smart_image = file_exists(DIR_WS_TEMPLATE_IMAGES . 'smartbg_' . $_GET[cPath] . '.jpg')?'_' . $_GET[cPath]:file_exists(DIR_WS_TEMPLATE_IMAGES . 'smartbg_' . (int)$_GET[cPath] . '.jpg')?'_' . (int)$_GET[cPath]:'';
} elseif ($current_page_base == 'page') { //add _page and ez-page id to bg filename only if ez-page id bg image exists, else add _page to bg filename only if general ez-page bg image exists
$smart_image = file_exists(DIR_WS_TEMPLATE_IMAGES . 'smartbg_page' . $_GET[id] . '.jpg')?'_page' . $_GET[id]:file_exists(DIR_WS_TEMPLATE_IMAGES . 'smartbg_page.jpg')?'_page':'';
} else { //add _ and page base to bg filename only if page bg image exists
$smart_image = file_exists(DIR_WS_TEMPLATE_IMAGES . 'smartbg_' . $current_page_base . '.jpg')?'_' . $current_page_base:''; //default/home page class will be just .smartBG, and filename smartbg.jpg
}// /Smart Backgrounds?>
<body id="<?php echo $body_id . 'Body'; ?>" class="smartBG<?php echo $smart_image;?>"<?php if($zv_onload !='') echo ' onload="'.$zv_onload.'"'; ?>>
<!-- EOF SMART BACKGROUNDS -->

<div id="mainWrapper">

I've added a link to my site in my signature.

Thanks