I cannot fathom out how to set the order of images to be displayed when you click on a category. They just seem to display in a random order. Not even alphabetically.
You can set the display order of the products as follows:
Search all the products for one category. Then click on the Edit Links in the table. Go to Category Mapping Tab and set Display Order. By default the display order is set to 1. Once you set the Display Order as N for a product, it will be shown as Nth Product in the list of products in that category.
This is for v1.30, hope it works in later versions.