You can't be a cheerleader or a mascot. You CAN have you sim wear the cheerleader outfit but nothing different happens. You might be able to do the same for mascot.. I'm not sure, but don't think so.

Sorority thing.. Haven't played in ages so this is off the top of my head, so might not be 100% accurate.

There are 2 different things. One is a group which you can get to through the phone.. I don't remember what it's called, but I think there's a different one depending on if the sim is male or female. Greek names or whatever.. Cappa Deltas.. that kind of thing. When you call them they all come round to your house and you have to make friends with a certain number of them. When you do, you move into their house. Don't remember what's that different once you have though.

The other is something like the Secret Society. I don't think you can know who the people in this are.. or maybe they all wear black with the llama on them? Don't remember. But you have to make friends with 3 or 5 of them, then a limo picks you up, and you can go to their house when you feel like it. Oh, and the people in it change in each game.. so no use getting people to post names. It varies.

Hope that helps.. like I said, might not be totally accurate, so apologies for that.