Poser renders certainly do not have to look plastic. Key considerations even more than lighting setup is a good bump map and specular map. The specular map is absolutely key to this in that specularity is "merged with the texture" so to speak. Specularity will be rendered with the small deformations present in skin texture. If specularity is applied without a specmap and bump map the render engine is just seeing a smooth surface and perfectly smooth is what your going to get no matter what lights you use. Also you can use blinn in addition to a specmap but do so sparingly.
The link is to an image in my gallery, its an example of realistic skin although the bump is set a little high in this particular image.
(It is a nude chest so if such things offend dont go there)[

http://www.renderosity.com/mod/gallery/index.php?image_id=1653412](http://www.renderosity.com/mod/gallery/index.php?image_id=1653412)