Currently, source packages are only available via anonymous CVS. See http://cvs.xemacs.org/ for details of checking out the xemacs-packages module.
(or a BSD compatible install program).
(3.75 or later preferred).
(4.2 from GNU texinfo 4.2 or later required).
A properly configured Local.rules file.
And of course, SXEmacs.
The packages CVS sources are most useful for creating XEmacs package tarballs for installation into your own SXEmacs installations or for distributing to others.
For a list and description of the different Makefile targets, See (lispref)Makefile Targets.