I read about the d3d sample for shadowing using stencil buffers (i think) but I though cards supported hardware shadows. I know the standard method uses shadow volumes and I think i know what they are, but can anyone clarify exactly how it works, and if shadowing a landscape in a terrain engine is feasible in realtime, considering the terrain has millions of polygons? John 3:16

Search through the archives for a few dozen posts on shadow volumes.

As for hardware shadows, do a web search for shadow buffers.