Prettygyrl,
I'll be more than happy to answer your question. It's an important question for anyone considering joining a Greek group in college--since getting an education is why you're going to school in the first place, not to pledge a group.
Many people lose sight of that, and it's important to remember, as well as to know what you'd be getting into before you start pledging. I know at my school, you have to have a 2.5 to pledge, and a 2.0 to continue as an upperclassman (pretty easy at my school because we don't have any grade lower than a "C"). I know that it's up to the individual chapter as to how long the "probationary period" is, basically depending upon what the school's guidelines for academic probation, expulsion, etc. Your school's Greek Council website (and in some cases, the Student Handbook) should clue you in on general guidelines for entering the Greek system (for NPC and NPHC groups). By the way, I don't think this specific question was inappropriate. It's a very important issue to be aware of, going into college and considering Greek life.