Let me first say that I have absolutely no knowledge of Poser (as in the capabilities) so I'm completely guessing here. But:

1) Isn't there an option to render to a format that supports alpha channels (ie tga or png)? For instance in Lightwave I can set up the render output to a rgb(a) format, but I also have to ability to render just the alpha channel to a file. This is particulary useful for postwork in photoshop.

2) Would it be possible to parent objects such as lights or camera's to the object, so that when you move the object, everything else moves with it. Of course if this is possible you do need to parent the camera, as well as the lights to the object. If you forget the lights shadows on the object will change when it moves.

2b) the setup to move the camera with the object is really unnecessary. You'll want to animate the object on the spot. This can be a bit tricky at first but in the long run it will benefit you the most. (see for example this)

@Paul. if you're asking for an specific example, WILL can probably help you out better, but in general the idea is to add a 3d object to a scene, set it to a certain pose, position the camera and render the object to an image, preferably with output to rgba format.

Anyway, I hope this helps a bit...