It really isn't that hard. Without going into the gritty details, it's really as simple as the following:
1) Hide all entities except the ones to be "shadowed".
2) Set the shown entities to a grey color.
3) Move the camera to the light source and point it towards your "wall". You should store off where the camera was.
4) Render this scene and capture it to a texture. (You should set up your wall to use this shadow texture at initialization.)
5) Reset the shown entities to their proper color/texture.
6) Show all entities.
7) Move the camera back to where it was.
1) Hide all entities except the ones to be "shadowed".
2) Set the shown entities to a grey color.
3) Move the camera to the light source and point it towards your "wall". You should store off where the camera was.
4) Render this scene and capture it to a texture. (You should set up your wall to use this shadow texture at initialization.)
5) Reset the shown entities to their proper color/texture.
6) Show all entities.
7) Move the camera back to where it was.