If you look at the page source, it is all HTML and javascript. It includes all the paths to all the images that it uses etc, theoretically it contains everything you need to build a custom HTML page to match the forum style. If you are running vBAdvanced CMPS, you can use the same trick to see how the pages there are constructed as well. To construct your own custom page you will need to reproduce the image folder structure or make sure the paths you use correctly point to where they are in the vbulletin folder.
HTH