The ACM (Association for Computing Machinery) is an international professional society (similar to the IEEE or IPENZ, for example). You might want to check the ACM Website for a detailed description of what the ACM provide; a brief description is that they run a digital library, sponsor conferences, that kind of thing.

The ACM like running student chapters in Universities, in order to increase their membership. WaikatoUniversity have one of these; basically, it's a group(similar in scope to the WaikatoLinuxUsersGroup, but with a general CS focus). It can do whatever it wants; previously we've had talks from a couple of CS professors and are looking after the organisation of the NextGenerationTour?.

There are chapters in heaps of other universities; in NZ, there's Auckland, Massey, Victoria and Canterbury.

I personally think it's counterproductive to have two of these things running that have a large overlap of people. It would be nice to involve them a bit more together.