Here is a update to an old script. Alot of 3D programs allow you to position your lights inside the scene using a visable control of some sort. This script provides this functionality to Zbrush.
To use it, load the Script, once loaded it provides a quick tool button in the Ztools menu.
1. Press "Select" this menu shows what lights are currently selected in your current Light setup.
2. Press the Light that you wish to Position.
3. The script will create a 3D sphere (if one isn't already present) and will place it at the current location that the light exists on the canvas. It will also color the light to the color of the selected light.
4. Manuver the sphere on the canvas and position it at your desired X Y Z location.
5. Press the "Position" button, this will set the currently selected light at that location of the sphere.
6. Repeat the above steps to position all the lights in your current light palette.
The display windows in the script will also report the Type, Intensity and Radius of each selected light for your information. Use the Light Pallette to modify or change any of the light parameters, add new lights etc... Then use the script to precisely position them in your scene.
Also I might mention that you can not position "SUN" type lights using this method, it will only position the Spot, Glow, and Point type lights.