279400 osCommerce Site Modification

We need the following done on our oscommerce power website: 1. Setup a discount for a repeat customer. Example we will like to give our loyal/repeat customers 10% discount. This discount only applies only for the products not shipping cost. Different customer can have different dicounts. 2. In addition to the above, if the product is already on a special (original price: 10.00, On Sale for: $9.00), then the above discount does not apply to that particular product price. 3. We need this as simple as possible, perhaps adding a discount variable to customer tables and then making the necessary change to the code. We should be able to set customer discount within admin panel. 4. Our website also also setup to accept coupons during checkout, so if customer has additional coupons, we have to make sure all the calculations are done properly. Thanks 2.