From Monolith Productions:
Now all you NOLF fans can customize your very own game. This package contains the source code for NOLF version 1.003.
To edit and build the source code, you'll need Microsoft's Visual C++ version 6.0 with service pack 3 installed, Microsoft's DirectX 8 SDK installed, and 400MB of available disk space.
To run your modifications, you'll need to have NOLF version 1.003 installed.