Is there a GJXDM User and Guide?

Yes, there is. The GJXDM User Guide can be located via the following URL: 
http://it.ojp.gov/default.aspx?area=nationalInitiatives&page=1083

Another good source of information is the GlJXDM Developer's Workshop Online Training Materials Website that contains all of the presentations, training materials, and recorded audio/video streams from the workshop held at Georgia Tech in Atlanta May 11-12, 2004.