The lightbox.zip contains js and css files that need to be copied to your dnn install root \js and \css folders to enable the lightbox slideshow on the product details page of the cart.
What is lightbox?
Lightbox provides users with a simple and elegant view of your product images without having to leave the product details page in the cart. When the user clicks one of the thumbnail images on the product details page the image magnifies using a gliding animation. The images automatically resize according to the size of the product image you upload in the product setup screen. Additionally, Lightbox provides a slideshow of your product images that allows users to scroll forward and back viewing your magnified product images.
Lightbox is a JavaScript application used to display large images using modal dialogs. For more information on the lightbox technology implemented in Smith Cart see the following link http://www.huddletogether.com/projects/lightbox2/
If you want to enable lightbox on the product details page their is a readme file in the lightbox.zip file that explains how to install it.
-Scott