Here is package with precompiled OpenMPI binary for Mac OS X. It is Intel-only, consists of both i386 and x86_64 versions (in the same way as universal binary for i386 and PPC). OpenMPi is compiled by Intel compilers and include interfaces for Fortran (Intel Fortran, obviously).
Package will be installed into “/usr/local”. Which means that you can find binaries in “/usr/local/bin” , libraries in “/usr/local/lib” and headers in “/usr/local/include”.