If it really is a Fortran 90 program (and doesn't make use of features outside of Fortran), you would just obtain and install a Fortran compiler for Linux and use that to build the program. Intel sells Intel Parallel Studio XE Composer Edition for Fortran Linux. There is also the gfortran compiler as part of the Gnu Compiler Collection (gcc) that should work if it is close to standard Fortran 90.
For a larger project with several source files, I have used Visual Studio output to list the sources files which helps create a makefile to compile the project on Linux. A previous forum article with an example makefile may be helpful:
Regards, Greg T.