I would like to know the easiest way to set up the following special or coupon in Zen, or what add-on is needed to accomplish the desired pricing;

I want to set up a special that offers free shipping if the customer purchases $400.00 or more from a selected category.
It would have to recognize the category and apply the free shipping. However if the customer purchases something from another category along with their order from the category with the 400 or more special all shipping costs are added to the order.

Is this possible