for the transparency, open your Render Globals, and make sure the image output is one that supports alpha channels (like TGA, since Photoshop can read it), and make sure the "Alpha Channel (mask)" checkbox is checked.
now when you render, all your geometry will be visible, but the background will be transparent when you show the alpha channel.

to get a shadow on a white surface i'd just make a plane and give it a white lambert shader, and then play with the attributes of the shader until it turns out how you want.