A shadow trick I've tried is rendering once over the background, and then again without a background, saving both in a format that includes an alpha channel (such as TIF). Import the second as a new layer into the first, load the alpha channel as a mask, and then insert a new layer between them and paint the shadows onto that. Play with blur and transparency to blend things together. It does need a bit of working out as to how the shadows would actually fall given the direction of the light, but it can improve on the results of Poser's shadow rendering. Tarot deck, though, I can't help you there. If you have a deck yourself you could perhaps scan in a spread and paste that onto a square prop as a texture?