How to approach someone at lunch?

So, I did ask a question about how to make friends at lunch. So I finally "faced my shy fear" and sat down with a group at lunch. So it's been a couple of lunches and our personalities aren't alike at all, all they talk about is their personal lives and their boyfriends and they talk in "secret code" because they probably don't want me to know. Well this hurts, and while I'm sittin with them I notice another group. This group are the "smart people", I'm in AP cles with all of them, but we don't talk, but I would like to approach them. They're a really big group, like 10 people, so how do I just barge in? I'm kinda nervous to how they will react to me coming in. So any suggestions would be great.