2 issues - PLEASE HELP: Item selected, others taken away? & Hitting Enter trouble

Issue 1:

How do I make it so if a customer selects one product a conflicting product option is taken away?

For instance on our cart there are options that would cancel each other out: www.kirkhammotorsports.com/cart for instance the polished car & brushed car options. If a customer selects one, how do I make the other disappear from the list of items?

Issue 2:

When putting a quantity in the quantity box, for instance the no. 1, I don't want it possible for the customer to be able to hit their enter button and have the item taken to the cart. The only way I want the item going to the cart is if they hit they "add selected products to cart" button. How do I turn this pressing enter function off? Thanks in advance! Rob