a PC theme, as in a style? (aka how you view the forum)
If you mean that, then generally you'd need access to a vbulletin forum where you have style permissions (admin), as well as a copy of PC's style info (which can be found in the style studio only for supporters, but if you were interested, I'm sure you'd be allowed to get a copy of that), but really, anyone can make a PC style. In fact, a few PC supporters actually have made styles, being Forgotten Memory and Gerri Shin. So in other words, yes you can if you have the resources.