I agree with KontrollerX. Girls in big groups are intimidating as hell for some guys. When I go out to the club, you'll see a guy and his wing circling the club. They'll only talk to girls that are either in a pair or a group of 3, but no more than that.
On the other hand, I don't agree with not talking to the friend. I wouldn't flirt with them until I know that the girl I'm interest in, is interest in me. I would definately make them a part of the conversation if things are going well. It takes attention from the girl you want. If she fights to get that attention back then you're golden!
Women know that when they're in a big group, it's intimidating. Basically that's their way of saying that they're not there to meet guys. On the other hand, there are women who are just plain stupid and will constantly ask themselves the question of "Why won't any guys come talk to me? Why is it so hard to find a good man?" when they're surrounded by 5 women whenever they go out.
I get a rush out of going into a huge group of women. I'm weird. 6/10 times I will get shot down. Definately not good odds, but I continue to do it anyway. The other 4 times, I will get shot down initially, then the girl will find me later and tell me something to the fact of how impressed she was by the fact that I would approach her when she's in a group so big.
Overall, I would approach and greet the girl that you like. Greet her friends. If she doesn't know you, introduce yourself. Then get to the point of asking her for her phone number. Conversations about life and crap can be had at a different time.
