Just a question

Hello, I just have a question and I will pay the first person to answer it $50. If a product is entered into the cart I need the cart to display and checkout based on a different customer group then they are logged in as. I want to change the customer group id to 6 IF sku w-100 is in the cart. I only want these changes to show on the cart page and it has to be able to checkout with the price tier associated with customer group 6. Please just tell me what files I need to edit and a quick run down of how to do it. It can be very basic but has to be detailed enough so that a semi-experienced magento programmer can understand how to do it. Simply bid $50 and IM me the message, I will pay the first person to clearly answer it. Thanks, Matt