Detailed steps on how to install FreeLing (and all required dependencies) are described in the installation section of the user manual
You can also check the Forum if you encounter any problems with installation.
Porting to other platforms
FreeLing library is entirely written in C++, using standard STL templates, so it can be compiled in almost any platform.
The natural habitat of FreeLing are Linux/Unix systems. Nevertheless, version 4.0 should be easily compiled on MacOS (provided you have libboost>=1.48) as well as on Windows (using MSVC).
The user manual also contains some instructions about compiling FreeLing on MacOSX.
To compile in Windows, follow the README file in the directory msvc of the source tarball.