to get started

add to .cshrc
 setenv PYTHIA8 ${OFFLINE_MAIN}/share/Pythia8
 setenv PYTHIA8DATA ${PYTHIA8}/xmldoc

login in a new window
cp the phpythia8.cfg to working area

you will need to add the HepMC node reader after the PHPythia8
to feed the hepmc node into GEANT4