Unfortunately there isn't much you can do protection wise to stop people from copying the photos other than to put a watermark on them which is always a good idea if you're dealing with graphics sales. Watermarks tend to deter quite a few of those that would download the graphics to use without permission as it will take a lot of work to try to get that watermark out and many people aren't that ambitious.
As for the gallery, this may help
http://www.huddletogether.com/projects/lightbox2/
This is a lightbox that opens a zoomed out box when you click on a graphic to show you a larger view (larger size graphic also should be watermarked). It allows you to setup galleries with lots and lots of links, no limit to how many galleries can be created so you could create a selection split up by categories or whatever.
The only downside to this is it has no way to see certain pics without having to go through the whole set that you have in a gallery setup because it has no thumbnail setups like Photogallery does. This means you need to make small galleries, maybe 10 to 15 pics each so they don't have to go through all of them just to get to pic number 45.
I am wondering what about Photogallery that doesn't fit in your site also? This would definitely be the better idea and you have the option to keep people from opening into large photos that can be copied directly.
Granted they should still be watermarked as many do know they can go in their temp internet folder and find most everything they have loaded on their screens, so they can usually get to them anyways if they know how. Watermarking is always your best protection.
If you need assistance with Photo Gallery, many of us have used it and would be happy to help you out. Keep in mind that you don't have to use a theme with it, you can choose to portray it any way you like and you can make Categorical galleries they can choose all from one window which would also be great for your site.
Anyways, that's my 2 ideas, Lightbox or Photo Gallery, either should do what you're looking for.