How do I make a partially transparent object block shadows?

I end up getting 2 full shadows, when I should get 2 partial shadows.

you can remove shadows on the lamp itself!

happy 2.5

What? But I NEED the lamp to cast shadows!

you mean soft shadows

you can play with some vars in lamp panel to get different shadows
also change the type of lamps
see wiki pages on lamp for shadows effects

happy 2.5