I have searched the forums extensively and have tried numerous options and am at a total loss. Please let me know if this listing should be placed elsewhere - I thought this was the best place for this question.

I am building a clothing store for a client. Many of the items have an additional image such as an image of a back of a shirt for instance. I am trying to figure out how to show the additional image to the right of the product main image on the product listing page. I have tried modifying code on tpl_modules_product_listing.php, tpl_modules_main_product_image.php, additional_images.php, tpl_modules_additional_images.php, and product_listing.php and I am having no luck on locating the code where I can make this happen.

Can anyone tell me how to accomplish this? It seems like it should be a simple copy of code if I can only just find where to paste it.