Hiya Dave,
A couple of observations, for what they're worth.
I notice that you are trying to include the 'Ribbon + Fullsize + Lightbox' in the detail for your item. Perhaps you should stick to using the 'Ribbon + Lightbox for PowerStore' - as it was purpose-made for putting in to PowerStore product detail pages.
Also, the paths on your page to the required components seem to be missing part of the path: i.e:
@import url("css/slimbox/slimbox.css");
@import url("css/common.css");
@import url("css/light.css");
<script type="text/javascript" src="js/mootools-core.js"></script>
<script type="text/javascript" src="js/mootools-more.js"></script>
<script type="text/javascript" src="js/slimbox.js"></script>
<script type="text/javascript" src="js/gallery.js"></script>
The /powergallery/galleries/ribbon_lightbox_powerstore/ part of the paths is missing (assuming you will be using the 'Ribbon + Lightbox for PowerStore' gallery).
I think you should swap over the type of gallery to 'Ribbon + Lightbox for PowerStore' and then click the 'Add to Site' button and copy the code from the code block in the 'Add to PowerStore' area at the bottom of the page to the the source view of the Long Description editor area in the product's update page.
The code you should be given by the 'Add to Site' page should be something like:
<input type="hidden" name="powergallery" id="1" theme="light" value="/full/sever/pathto/yoursite/thegraphiclibrary.com/shop/powergallery/galleries/ribbon_lightbox_powerstore/index.php" />
The bit in grey will be different, being particular to your site.
Cheers.
