Hi,
Ecotect should run fine under Vista. The only issue is with the screen snapshot function when you are running the Aero theme as this uses complex desktop composition to overlay 3D OpenGL canvases within the desktop as opposed to actually direct embedding. Thus, we have added an additional option in the Display >> Copy to Clipboard menu to enable/disable 3D composition in Aero. When you want to take lots of screenshots or create a movie and you use Aero, it is quicker to disable the 3D composition first. Even if you forget to re-enable it, Aero will revert back when you close the instance of Ecotect you used to turn it off.
Regarding Radiance, this too has been tested pretty rigourously in Vista. As long as you have located where Radiance is installed and got green ticks in the export wizard, you should get something when you run Radiance.
Is it possible for you to post the text or an image of any error messages you get or of the DOS prompt displayed when Radiance is run ? In the export wizard there should be an option called 'Pause on completion' - make sure this is checked to keep the DOS prompt up when the run is finished so you can read/copy the output text.
Hope that helps...