Selecting the Shadows check box in the Light Editor of a light that supports shadows (point, distant, spot, sky, sun, projector and goniometric) results in the selected light casting shadows in the scene. Shadows will only be visible in photorealistic renders, unless you are using a Hardware accelerated OpenGL 1.5 compliant graphics card, in which case, you can preview interactive shadows. See Presenter Page for details on how to display interactive shadows and lighting.
In addition to choosing which lights in your model will cast shadows, you may also select which geometry items in the model should cast a shadow. Each item in the scene has its own shadow casting option.