Ok, I know this is a beginner question, and I've actually done this before, I just can't for some reason remember how.

What I need to do is render each object in the scene to a different photoshop layer. Each layer much keep the shadows cast on it from the other objects. I really can't remember what the process is for this, and Google isn't helping much. I'd like to do this with mental ray also, if possible.

I've tried putting each object on a different render layer, and selecting "render all layers" - but this renders each layer separately - which is not what I want.

Thanks much for the help in advance.