You could use the zen_get_products_category_id function, which retrieves the product's "master category id".
Code:
$category_id = zen_get_products_category_id ($_GET['products_id']);
Depending on the number of "special processing" categories, you'd set up arrays that contain the master-category-id of the associated products, e.g.
Code:
$special_list1 = array (1, 2, 3, 4);
$special_list2 = array (5, 6, 7, 8);
and then check to see if the current product's category id falls into one of the "special" ranges:
Code:
if (in_array ($category_id, $special_list1)) {
$tpl_page_body = 'tpl_special_list1_info.php';
} elseif (in_array ($category_id, $special_list2)) {
$tpl_page_body = 'tpl_special_list2_info.php';
}