I'm struggling to get the _MED, _LRG pictures displaying properly.

I've only done it for a couple of products and normally would refrain from posting a link due to the nature of my site but can't really explain it very well otherwise:

http://pleasureme***toys.co.uk/toys-...-prince-purple

(replace the *** with a well known adult activity)

The thumbnail is displayed fine in the category listing, the _MED shows up fine on the product page at 200x200 but if when you click on the larger picture, it's showing the thumbnail first and the larger picture after as an additional image. Ideally it should only be displaying the large image or at the least, the large picture first and then the other sizes.

Can anyone help?