Presenter will be installed as a plugin for Powerpoint, and its first function is to convert the PPT presentation into a SWF-file. But is is much more than that:
you can insert video, flash files, Captivate generated SWF's, audio
you can add a quiz, there are quite a lot of question types available
it has some fine added features: Table of Contents, with a Search function, Notes...
it works perfectly together with Connect Pro; if you ever had a meeting/seminar in Connect Pro, you'll almost certainly have seen a Presenter presentation
you can publish to PDF
Personally I'm using Presenter as a sort of wrapper, based on a presentation but with Captivate or Flash generated SWF's (interactivity is preserved).