I met this girl and got her number, called her up and she invited me out to hang out with her and her friends this weekend. I think it's pretty clear I'm interested in her, we exchanged screen names and her info says something that indicates she has a boyfriend. What's that about?
she might have a boyfriend. but it might be about you. depends on what the screen name is. if she has a boyfriend then she probably thought you were cute and gave you her number just in case they broke up or something
Maybe you should go and test the water to see if she had a bf, maybe they just broke up or even a while ago and she hasn't updated it. Let her see you as a friend first gain some trust and then maybe later it can develop into something more. If however it doesn turn out that she has a boyfriend and you have feelings for her the sensible thing to do is walk away no matter how much you might like her.