I don't have any knowlege of Antville, but here's what I know about MT.

If you want to point us to the documentation on this feature in Antville, maybe we'll be able to give you a more direct answer. A quick browse through
their site and I still didn't find anything about authors.
You can set up how ever many users/authors in the MT system as you need. When you set them up as an author, you select which options they have access to. Then they can post entries to the log.
Does that help?
Kristine