Incorporate XML inventory feed into our OSCommerce website

My manufacturer provides a realtime XML inventory file that perfomrs a querry on inventory levels for their items when the item is viewed from our site. We use the same model numbers as the manufacturer. We have the XML inventory feed working on our Windows based .ASP site, but can not figure out how to make it work on our Linux based .PHP Oscommerce site. Need someone to program it so that the inventory quantites for our products are updated automatically using their XML feed. (Will also require a means to not queerie inventory for products that do not come from that manufaturer. (They get upset with us if we hit their servers with queeries for products they do not supply us with)