[funkydunk]

I did a slight variation on this which shows the first detailed product image instead of the thumbnail.

First I cretaed a new template in modules/detailed_product_images/product_images_main.tpl

{if $images ne ""}
{section name=image loop=$images}
{if $images[image].avail eq "Y"}
{if $smarty.section.image.index eq 0}
[img]../product_image.php?imageid={$images[image].imageid}[/img]
{else}
{/if}
{/if}
{/section}
{/if}

Then amended the product.tpl template to show the code below where you want the detailed image to show:

{if $active_modules.Detailed_Product_Images ne ""}
{include file="modules/Detailed_Product_Images/product_images_main.tpl" }
{else}
{include file="product_thumbnail.tpl" productid=$product.productid image_x=$product.image_x image_y=$product.image_y product=$product.product}
{/if}

This will show the detail image if there is one, if not then show the thumbnail and if there isn't one of those then the standard no image icon will appear. You will need to load a new personalised one up.