A little bit of customization for the shopping cart. Ajax & Java Script programmer needed.

I am building a simple presentation site for the client and there will be a shopping section with 4-5 pages/categories. What I would like to have is that the shopping cart content is constantly displayed in a block somewhere within the page while the customer browses shopping pages and adds items to the cart. Please see how it works at www.computers360.ca. When you click "add to cart" for any item on the page, there is a small animation adding that particular item to the cart which is displayed in a left column box. If you decide to add more items, they are added to the same box and there is NO loading of the new page unless you decide to either go to the cart only or to check out (go to paying). What I also need is for the customer to have option to choose or specify color or size for the item they choose to buy. It is actually clothing what they will buy from this site. And, there should be and option on the merchant's end to approve discount for the entire merchandise when she receives the request from the shopping cart. Shopping cart is to be working with PayPal only. Thanks for bidding.