I have once and for all squashed some bad bugs in my RADex script, so that cameras work correctly and also mesh sizes. I have added mesh smoothing, RIF file export (more OS portability), and HDR Image Based Lighting.
Go here for basic tutorial and all download links:
http://mywebpages.comcast.net/rayae1/tutorial.htm
Here’s a taste of the new features, Suzanne as smooth as she gets:
Looks Promising… I d/loaded Radiance awhile back only to find out I needed Auto CAD. 
If you downloaded Desktop Radiance (for windows), you only need AutoCAD if you want to install the integrated components. In the DeskRad installation, only select “Radiance For Windows.” This installs only the base binaries for Radiance, and that is all you need for rendering. Also, if you are a masochist, you could try to compile with Cygwin. I’ve had only partial success with that.