This is a quick way to use Cycles to light your scene realistically, while using materials from Blender Internal. What I have done here is a continuation of this blend: (http://www.blendswap.com/blends/node-setups/cycles_internal-blend/) BUT makes use of the new cycles render layers to combine the final image
My apologies, to get this to work, just connect the Brightness/Contrast node to the composite and render. The "Combined" scene must also be active for this to work. :)