Try to replace most infinite lights with spots. Move them very far away (500-1000 Y, -1000 to 1000 Z. -50 to 50 X, for example) but pointing to the middle of the scene. Infinite light is not stopped by solid objects. But a shadow is an unlighted area. Poser 6 users may use point light instead of spots. One pointlight and a spotlight near to the camera, both in raytrace mode, is enough for most scenes. Low memory usage and fast rendering :)

---