bbPress.org

In theory you would make a backup of your my-plugins and my-themes directories. Then, delete the files in your existing bbPress install. Next step, run through the famous “5 minute install” of WordPress, and download the bbPress plugin and activate it. That’s the obvious part.

I would assume that a bbPress plugin would create a new top-level menu in the WordPress admin area. In a brand-new install, this would allow you to create the bbPress specific data structures in your database or to migrate existing bbPress data from an old version. After that step, the bbPress admin menu would switch to showing admin options for forums / topics / posts, etc.

My guess (if data structures remain largely the same) is that the “installation” of the plugin would merely write a WordPress option value telling the bbPress plugin what its database prefix is, and all the data already there would appear automatically.

Assuming that a bbPress plugin is connected to its data, it would need to be connected to the GUI somewhere. My guess is that you would create a WordPress static page and its content would be a short-code that the bbPress plugin replaces with its entire display.