Apple doesn't have any kind of fortran for Mac OS X / Darwin. However, various flavors of fortran are included in various flavors of GCC. You can use MacPorts to install GCC 4.1 (I think GCC 4.2 is still developmental). Someplace useful to you at some point is 
http://gcc.gnu.org/wiki/GFortranGettingStarted. I know that I've compiled other peoples code that contains fortran (R language for statistical computing) under MacPorts. With that said, MacPorts doesn't seem to find the direct command to start the compiler (gfortran). I suspect you will need a 'portfile' to get this working. For my part, I haven't written fortran since ... 1977.

Chuck

On Jun 2, 2007, at 12:44 PM, macports-users-request@lists.macosforge.org wrote:

Message: 9
Date: Sat, 2 Jun 2007 12:44:43 -0400
From: Andre-John Mas <ajmas@sympatico.ca>
Subject: Fortran
To: MacPorts Users <macports-users@lists.macosforge.org>
Message-ID: <5F50DAC7-F5D7-4A03-89D3-C9BE61BFABFD@sympatico.ca>
Content-Type: text/plain; charset=US-ASCII; format=flowed

Hi,

I have just been given some fortran source, which I need to compile,
so I was curious to know whether a fortran compiler existed as part
of MacPorts? There doesn't seem to be a Fortran compiler as part of
the basic gcc installers that comes with XCode, at least there doesn't
seem to be an f77 command.