lol, I made a copy of your main page, then tried to guess the path to your host root to see if the code would work on my host, of course it failed misserably, but hey I was trying to help.
ok, here is a little information.
Jgallery is an entirely seperate gallery system, when I say it integrates with Zencart, it only makes the gallery function within the cart as if its part of the cart. I added the mod that gives you the uploading ability to the zencart myself, simply to enhance the integration.
Now, uploading everything, does not overwrite any file unless you already have a folder called gallery, that said, the upload folder it creates is in the root of your host and is called " gallery " not Gallery or JGallery, jGallery or any other variation on that theme.
So, the code above needs to reflect the name of the gallery folder. If you decide you want to have a gallery folder thats called imagegallery, thats fine, rename the gallery folder accordingly and edit the code you inserted into the page of zencart.
It does work, but, it DOES NOT work if you use SEO, so you must add the page your using to the NOT include for SEO option for it to work.
I can say with all certainty it works well.
My wifes css for her gallery I edited to remove almost everything so all that is left is the images and nothing more.
hope this helps, but if not, please feel free to email me direct or skype me ( spottedhaggis ) im online much of the time