Well, as I said in my first post, I want the 3d library to make it easier to check collisions, do some picking etc.. Basically, I want to set up a scene graph, add a bunch of "Entities" (extending BranchGroup) into it, check for collisions, do movement and picking, then send data to the clients about what Entities are where, if they've taken damage etc etc.
The collision detection and movement can't be done on the client (would be a cheaters paradise

), so I figured the simplest solution would be to set up a 3d library of some sort on the server and let that handle that stuff (I really don't have a clue how to write that myself).