It really depends on how low you are talking about. They look at how hard your classes are, what grade you achieved in them, and your overall GPA, if you have below a 3.0 it is going to seriously affect you, however if your essay, SATs and extra curriculars are outstanding, it might help. If not, you will not have a very good chance I am sorry to say. Audition will not carry you over the top, it needs to be the whole package, and don't give excuses about your grades during your interview or on your app whatever you do! Good luck though, everyone has a chance and there is no harm in applying so don't get discouraged, but be realistic at the same time, if you got all D's or F's your first two years, there is really very little chance you will be accepted, even though your later years are more important, those first two really do still count! If you don't make it take some course at a local college and get your grades up and try again for next year! Don't get discouraged and good luck!
"That boy could use some Prozac"