I used the plugin that Lynn and Opserty showed me in the thread I linked you to earlier, to create the custom posbit. I just created a new template called
postbit_ygotas and followed the instructions they showed me. You'll probably have to familiarize yourself with the inner workings of the postbit templates, but it's not that bad.
You don't have to install a new forum to have more then one style. In the case of The Abridged Series up there, I'm just using my normal style with the plugin. In some other parts of my forum, I'm using a different style along with the plugin. You might want to give the Styles section of the manual an overview as it will clear up a lot of things for you:
http://www.vbulletin.com/docs/html/styles_and_templates