modifiy some features on our Oscommerce store

This is a small project with the following requirements for the modifications: 1. when clicking the main product category at the left menu at homepage, it should display the subcategories immediately but not refresh the pages as we do now. 2. We apply the shipping policy of free shipping on orders over $ 150. But you should modify the shipping module like this: it allows the administrator to set the different shipping cost for different kinds of products and set different free shipping policy. That's is, the shipping cost for some products is $19.99 ( no additional cost per extra product), free shipping order on order over $150, but for some products, the shipping cost is $45 , extra $ 25 for each additioanl product...etc. Free shipping on order over $500..., but it can allow the adminstrator to set no free shipping for this kinds of products,etc. 3. add rss.php. P.S. All your work should not affect our website alive. Payment should be sent after this project have been done perfectly.