If you are familiar with installing software on your PC and know lots about the Windows system you can try to install g77 from the link below. You should read the instructions first to see if you understand the instructions.
Below is a link to Fortran (g77) for PC:
Below are alternative instructions (these require about the same amount of knowledge as the instructions above).
Alternative is to add cygwin to your PC (linux running on PC). Download cygwin from http://www.redhat.com/services/custom/cygwin/
Use cygwin_setup to get gcc, g77 and nedit.
Also needed is
which is the Windows X-window system. (Needed for nedit)
When using X-windows from cygwin you need to add at the terminal prompt
setenv DISPLAY: 0.0
(this allows programs such as nedit and xterm to open windows).
Installing Fortran gives instructions for installing gfortran on a PC.
Nedit can be downloaded from
gfortran downloaded from http://hpc.sourceforge.net (see links with gfortran in name).
Fink commander is a great utility to install to get lots of linux packages for the Mac.