Filter Module BS
This following module is based on this Addon.
All credits to the original coders.
This is for osC 2.3.4 BS GOLD and/or EDGE version.
It will give you the possibility to "narrow down" the products listed in the product_listing.php page.
To setup filters I think you better install the sample filters and look how they are setup.
Please backup your files and database before attempting to install this.
There are unfortunately core code changes necessary but really minor ones.
Support Topic: http://forums.oscommerce.com/topic/408337-products-filter-bs/