The FAQ is on the web:

  http://www.newplanetsoftware.com/jx/faq.html

Important notes:

  There is a separate FAQ for each program.  Look in the appropriate
  subdirectory of the programs directory.

  Source distributions that unpack into different directories (e.g.
  JX-2.1.0 and JX-2.0.0) are guaranteed to be incompatible.  Contact the
  developer if the program that you want to build does not unpack into the
  latest version of the JX distribution.