I'm also trying to work out how to click through to display a larger image for the detailed images so I would be very interested to see if anyone has already done this. It seems like a basic thing that you would expect in a shop.
I'm stuck though - I can set up a new template to display the image larger. But I want to pull that template in when someone clicks on the image. So I thought I would add the image to the string inthe URL and then be able to check somehow for it. However, when I tried to put &image={$images[image].tmbn_url} or something else into the link
<A href="product.php?productid={$products[product].productid}&cat={$cat}&image={$images[image].tmbn_url}"> I get error 33 you are not allowed to edit that resource.
Any help would be greatly appreciated.