Scott,
Flash would be the perfect solution to keep people from downloading the images. Essentially you would have to make the whole photo gallery in flash though, and embed the exported .swf file in a basic HTML file.
This is a good tutorial:
http://www.kirupa.com/developer/mx/photogallery.htmAlso you may want to check out the FAQ and Web Site Design sections on our Flash-Template-Design site:
http://www.flash-template-design.com