Development on the buying process in osCommerce

We want a development on the buying procedure on our online bookshop: [login to view URL] Our goal is: when the client adds to the basket a product/s we previously marked as a special one/s, at the end the delivery expenses turn 0 so the shipment is free. It doesn't matter other products not marked as specials are also included in the basket, if a special one enters the basket the whole order generates a free shipment option. Platform: osCommerce Changes in the standar sales procedure: - How to add a product that is already marked as free-delivery product to the basket. If the client adds to the shopping cart a Free shipping product the at the stage of 'Shipping Methods' (in spanish 'Formas de envío' see attached picture) a new shipment option will be generated. It will be called 'Envío gratuito promocional' (it means Promotional Free Shipping). This option will be at the top of the other delivery options and it will always be checked by default. So if the client wants another delivery option he will have to uncheck this one and then check his selection. A text of one or two lines will be under the title of this Promotional Free Shipping as it is with the other delivery methods. - How to suggest a Free Shipping product during the buying process. If the customer buys a product that is not marked as 'Free Shipping' when he get to the stage of 'Shipping Methods' only standars delivery methods will be showned. However, at this stage, between the 'Delivery Address' (in spanish 'Dirección de entrega') and the 'Shipping Methods' ('Formas de envío') we want to embed an slider that will display several of these 'Free Shipping' products. The slider should be very similar to the image we attach with every book displaying image of the front cover, title and price. This slider will serve as a reclaim. Above the slider there will be a title and explanatory subtitle. The customer may click on any of them and go to the Product Overview. After reviewing the product the client will click in the 'Comprar ('Buy') button and the product will be added to the cart. The client can still buying products or return to the 'Shipping Methods' stage with the new delivery option added to the Shipping options. - Visibility on the web. The books tagged as 'Envío gratuito promocional' ('Free delivery') should be highly visible on the web in two spaces: 1. 'Product Overview'. This may appear above "Customer Rating." A striking text indicating that shipping is free if the book is added to the cart will be showned. We still have to write down the concrete text. 2. 'Product Listings'. When clicking a cathegory, filter or a search a list of products is showned. At the right of every product we have a few buttons: 'Comprar' (Buy), 'Sin stock' (No stock) and 'Avisar stock' (this is an alert to the client can ask for a product with no stock at that time). The client can only click on the first and the third one, the second one is only informative. We want to add a new button or banner that says 'Envío gratuito' ('Free shipping') followed by a short explanatory subtitle. Finally, keep in mind: - This feature will be enabled for customers whose shipping address is in Spain. Shipments to destinations outside the country should be left out of this 'Free shipping' alerts and shipping option. CANDIDATES SHOULD HAVE AN EXTENSIVE EXPERIENCE IN OSCOMMERCE