Ah, yes, I get asked this question more than any other. Look here and here, for example. If I may be so bold, you may want to check out a Squirtonline survey, "How to Tell If Someone Likes You." But I don't mind answering this again because every sitch is a little different.
Now what does all this playing around mean? Well, not very much. She told you she's not available, dude. Nothing else she says or does after that really matters. So she gets her jollies by freaking with other guys. Gee, that's great and all, but if you're looking for something more you're barking up the wrong tree. I don't care if she's always hanging around and talking to you. Poaching someone else's girlfriend is not cool.
I will make one exception. If you're sure she's "the one", if you can't imagine life without her, then you owe it to yourself to let her know how you feel. Leave the ball in her court. But I know that's not what's going on here, because you didn't say anything like that.
There's nothing wrong with flirting and "playing around" (I'm assuming this doesn't mean "fooling around") as long as everyone is clear on the rules of the game. Some people need the attention. Bottom-line, if you're looking for a girlfriend you're wasting your time with this one.
à tout jamais,