Sorry for raising a dead thread, but i had the same problem and solved it. I've searched for "qcad help segmentation fault" and this was a hit.
Qcad needs his application directory as the current working directory. Say your installation is under /opt/qcad you can't link /opt/qcad/qcad to /usr/bin/qcad to get it in your path and you can't start /opt/qcad/qcad when you want to use F1-help.
Solution: build a simple quick'n'dirty wrapper script
exec ./qcad $@