OK, I've been adding the new columns to the queries I found in default_filter.php, for example:
PHP Code:
// We are asked to show only a specific category
      
$listing_sql "select " $select_column_list " p.products_id, p.products_type, p.manufacturers_id, p.products_origin, p.products_make, p.products_design, p.products_price, p.products_tax_class_id, pd.products_description, if(s.status = 1, s.specials_new_products_price, NULL) AS specials_new_products_price, IF(s.status = 1, s.specials_new_products_price, p.products_price) as final_price, p.products_sort_order, p.product_is_call, p.product_is_always_free_shipping, p.products_qty_box_status
       from " 
TABLE_PRODUCTS " p left join " TABLE_SPECIALS " s on p.products_id = s.products_id , " .
       
TABLE_PRODUCTS_DESCRIPTION " pd, " .
       
TABLE_MANUFACTURERS " m, " .
       
TABLE_PRODUCTS_TO_CATEGORIES " p2c
       where p.products_status = 1
         and p.manufacturers_id = m.manufacturers_id
         and m.manufacturers_id = '" 
. (int)$_GET['manufacturers_id'] . "'
         and p.products_id = p2c.products_id
         and pd.products_id = p2c.products_id
         and pd.language_id = '" 
. (int)$_SESSION['languages_id'] . "'
         and p2c.categories_id = '" 
. (int)$_GET['filter_id'] . "'" .
         
$alpha_sort
To no avail.

I can't get it to look in those columns and spit out results.
I think maybe I need some guidance on this one.

What needs to be rewritten and how would it be rewritten?

Please help..

Thanks in advance,
Alli