How to make a graph like this

http://www.sapdesignguild.org/commun.../net_graph.gif

I want to be able to generate graphs similar to that one, any help would be nice.

Thank you.

Never used it, but take a look at JGraphT - a free Java Graph Library
Also, while not java, I've used Graphviz with excellent results.
Other than those, google "Rooted Tree Drawing Algorithm".