Per your network, 3D engine, server, ODE, and (open source) license questions ..
As Jon Said:

"Check out Croquet...

http://www.opencroquet.org

I think that will answer all your questions. And yes, it is implemented in
Squeak."

Here is list server info for the project:
http://croquetproject.org/Community/listserver.html

Cheers,
Darius