Following Graham's instructions, I was able to download G95 successfully onto my Mac. Here is what you do:
Go to http://g95.sourceforge.net and download "Powerpc OSX Binary" and "cctools"
For cctools, it will bring up a window and walk you though the install. You may have to give your password to have permission to do this. (If you still don't have permission, then you will have to get the owner of the machine to do this) For the g95 part, it will come as "g95-powerpc-osx.tar" and should automatically create a folder called "g95-install" on your desk top. The executable version of the compiler is called "powerpc-apple-darwin6.8-g95" and is in g95-install/bin. You should move the g95 folder to one of your /bin folders. In my case, I put it into /sw/bin. I then put a link into /sw/bin so that typing "g95" will link to the actual g95 two levels down, i.e., type
ln -s /sw/bin/g95-install/bin/powerpc-apple-darwin6.8-g95 /sw/bin/g95
In my case, I did not have permission to do this at first, so I had to use the superuser (sudo) command:
sudo ln -s /sw/bin/g95-install/bin/powerpc-apple-darwin6.8-g95 /sw/bin/g95
This worked after I gave it my password (in response to the prompt).
At this point you should be able to type "which g95" and it will point to the right place.
Finally you will need to change the Makefile in your Fortran directory to link to the new compiler, i.e.
%: %.f90
(tab) g95 -C $< -o $*
%: %.f95
(tab) g95 -C $< -o $*
Let me know if you have any problems getting this to work.