Free TShirt with certain dollar amount

I need to setup my store so that clients who spend $24.95 will receive a free TShirt. I need to be able to have them select a size also. How can I set up my store so that when they purchase this amount they will be redirected to a page where they can choose a size of TShirt. I am thinking it might have something to do with attributes but my brain is just not coming up with an answer. Thanks

This does something like that (I don't know about the size thing, but if it's just another product, attributes should work).

http://www.zen-cart.com/index.php?main_page=product_contrib_info&products_id=1145

Search the forums for info about the mod before you install it. I'm not sure how stable it is.

Wonderful! Thank you so much.

The Dangling Carrot mod has problems and should not be used at this time.