Cloud Generator Question

How can I generate clouds with an alpha channel in order to key them over a previously rendered scene. When I set the output to png with RGBA and transparent sky, the clouds don’t render. I want to key clouds over a landscape fly-over.

Second question, how do I keep my bounding box from casting a shadow?

In the render panel uncheck sky under layers option.
To stop the bounding box from casting a shadow, go into the material options for all the objects it is affecting, and under the shadow panel, turn on receive transparent.

Hope this helps

thanks for the help, mslarsen!