The latest packaged releases are available at http://www.extreme.indiana.edu/soap/xpp/ and the latest source (if you want to be on the cutting edge) can be obtained now from anonymous CVS at:
cvs -d :pserver:anonymous@cvs.extreme.indiana.edu:/l/extreme/cvspub login CVS password: cvsanon cvs -d :pserver:anonymous@cvs.extreme.indiana.edu:/l/extreme/cvspub co XPP3/java
If they relate directly to the implementation, build or bugs them to XPP3 mailing list (XPP3 is part of XGWS) or if question is implementation imdependent and is about XmlPull API questions to XmlPull discussion list.