Available in 3.0:
For the most basic visualization, all you need to do is call the Model method setUseVisualizer() prior to calling initSystem():
// usual stuff ...
This should result in a graphics window popping up with a reasonable display of your model in it.
For more information, look in the OpenSim API's Doxygen documentation for the ModelVisualizer class. For advanced users, OpenSim::ModelVisualizer is based on the SimTK::Visualizer class that you can read more about in Simbody's Doxygen documentation.
More to come ...