The latest version of my VisioAutomation library has been published on codeplex: http://visioautomation.codeplex.com/
Because there are so many components, I’ve drawn this conceptual map to help you see which pieces are useful for you.
I have started (*started*) documenting the project here: http://cid-19ec39cb500669d8.skydrive.live.com/self.aspx/Public/Visio/VisioAutomation/VisioAutomation-Developer-Guide.docx