As a still photographer who sometimes works with multiple off-camera lights (strobist-style) I would love to be able to experiment in software to see a very close approximation of how a setup would look.
In all seriousness, go download a build of blender that has the GPU renderer built in. It is totally handy for what you are talking about. Hit me up via my email in my profile if you want help getting started, the interface can be a bit non-intuitive.
I have a plugin for Cinema 4D called "HDRI Studio Kit" that is basically a set of predefined studio lights and lighting setups. Makes it very simple to light objects using traditional photographic methods. You have various tent setups, soft-boxes, umbrella lights, etc...