It's packaged as a complete plugin that can be installed through the Plugin Manager. It uses the Gossamer libraries where appropriate and doesn't rely on any CPAN modules. I wrote a lightweight NNRP class and a lightweight Article class.
There are a few optional CPAN modules you can use if you like. The plugin will automatically detect and use them. One is URI::Find which will automatically hyperlink url's in messages. The other is Date:Format which does a better job than the built in Gossamer one.
It works very similar to the MailArc plugin including formatted quotes (which are configurable and use standard GForum codes), fully threaded etc. Usenet users are created as special users to allow searching by username. These users are created only in GForum so they won't interfere with Community users. The usernames are intelligently created based on their email address. This means if a posters email was "Paul J" <email@example.com>, then a user would be created with a username of Paul J and an email of firstname.lastname@example.org.
Give me a few days and I'll post it here. As I mentioned, it doesn't send outgoing posts, but I will get around to adding that eventually. Alternatively, feel free to hack around and add it yourself. :)
I'll see about getting a demo up over the weekend.