Composite + Objects with transparency

Good day everybody,I’m very new to the Blender World and was able to solve most of my questions by reading this forum and viewing a lot of great tutorials.At the moment I’m stuck on getting a transparent object merged with a background movie. I’ve attached a screenshot how my scene is put together. I’m talk about the windscreen of the spaceship. This object has a tranparent material but the spaceship is rendered without the background.Any ideas what piece I’m missing ?I use Blender 2.73 with Cycles.

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I noticed that the windscreen shows transparency. But from the road (middle render layer in the above screenshot).I see two options to get rid of the plane, at which the shadow from the space is dropped:a) I change the size of the plane to fit the shadow and move it along with the spaceship in the animation.b) I make the windscreen ignoring the plane and make it using the backgroud movieAm I right ?a) seems quite simpleb) is this possible ?