First of all I want to say that I think that it is very possible that your friends are indeed Christians as they claim. No Christian ever lives like God is #1 in their life all the time - it's simply impossible to do. Everyone makes mistakes, everyone struggles with sin, and everyone is guilty of putting other things before God *repeatedly*, including Christians.
For your friend with a problem with inappropriate contentography - if she admits the problem and wants to rid herself of it (which is sounds like she does, but has never been able to by herself), then try to get her to agree to an accountibility system. There are a number of free computer programs available that help keep people accountable to a friend, relative, pastor, or whoever - for what they are putting in front of their eyes on the computer. Lust is a very difficult thing to battle by one's self - I've found that accountability to others and accountability to God are the best methods to helping that situation.
For the friend with the drinking and partying problem - I think that this is more serious. This is a lifestyle conflict. You've got to put your foot down and make sure that she knows that you firmly believe that that kind of lifestyle is not a godly way of living. Drinking, partying, and hanging with the wrong crowd is a HUGE stumbling block in one's relationship to God. If she knows this, but does not have the desire to change, then she needs to re-evaluate whether she should continue calling herself a Christian. However, if she does have the desire to change, then there are a number of things you can do. It's very difficult to get out of a habit of drinking or a habit of hanging out with certain people. I'd suggest first to pray for her, perhaps pray together, that God would help her change. Secondly, you could try to help her ger more involved in activities within the church. Being a Christian isn't boring. There's plenty of fun things to do and plenty of important things to do. Help her get to know a better group of people to hang out with. If you need to go to a person of authority in the church to help her out, go ahead - they're there for a reason.
Hope that helps