Actualy, that's a misnomer. Unfortunatly, it's too late in this case, but you can copyright a design, but it has to be noted. Otherwise the copyright generaly only applies to the content.
I took a peak at their source code, and I've got an idea. They are still using the same banner image that you are using (hot linked to your site no less!) I say rename it to something else and change your site to use the new name. Create a new image, give it the old name, and have it say (in big red letters) "THIS IS A PIRATED WEB DESIGN!"
It's just an idea and sure to get someone's attention.