How do I build it? The documentation is really shady about this. It says you need to place scons.py into the directory, but I have no idea where this is. I have tried using the included prebuild, but it did not produce any .lib files.
No need to use scons.
After you download the jsoncpp source, like from https://github.com/mrtazz/json-cpp, unzip the sources. In this unzipped source tree, under /makefiles/vc71/ you will find several Visual Studio project files which you can up convert and build.