If you want to use your G4/G5/Intel Mac with OS X for some good numerical work .. this could be useful to you. I have here, binaries, source, documentation and instructions to install Fortran, MPI, OpenMP, PVM, Octave, GDL, Cactus, Globus, RNPL, GIMPS, GRAVSIM, FEYNMAN, Xmgr Grace, GNU Java, etc. on Darwin.