Anyhoo, the project has necessitated some additional code not directly linked to the project, which I can release. The first one is a Simple Physics Library for jMonkeyEngine.
jMonkeyEngine comes with an excellent physics engine. However, it is almost too excellent, and has a lot of features that I don't require which takes up CPU usage. In addition, a multiplayer networked FPS requires the ability to "rewind" time on physical objects, which the existing JME physics engine can't do.
The full source is available here, which includes an example "first-person walking around" game.
And here is a video showing it in action.