It's really not about posts; Craig messed that part up when he took off the post count in the General Discussion section. However, I would say that a regular is someone who logs in fairly frequently, and has been around longer than a month. I consider an 'old timer' (As KZ puts it) as a forum goer from the old forums, even ones who joined near the end, of which there a precious few.
Still, if you manage to post over 200 times, I'd say that you are, if not a regular or old timer, then at least no longer a newbie.