Is there some type of online network where class notes, power-points or other class materials are posted? If so, can it also be used for conferencing with other students and teachers?

Some classes will have Avenue to Learn, profs may post the slides/notes before class. There are also discussion boards for students/profs/TAs to use. Not all courses use it, but most larger classes do.

There are also some profs who will have their own website where they post lecture notes and stuff. If they do, they will usually give you the link on the first day of class.