Don't know about disabling the right-click. I notice that you cannot copy an image that you use in the background. If an image is placed in the background using CSS, you cannot right-click and save image as. But people could still print screen and copy the image. There's another way to stop people from stealing and that is to watermark the image. I know this doesn't answer your question but i hope it helps you in other ways to prevent people from stealing.

Kenneth