I've released a Microsoft Windows version of the Ruby real-time computer vision library HornetsEye. Now HornetsEye not only runs under GNU/Linux but under Microsoft Windows as well! Currently Hornetseye for Windows is pretty basic since it does not have Video-I/O and cannot yet display images without the help of Qt4. If you are still interested you can already download a big package with installers for Ruby, HornetsEye, Qt4, and a lot more. See installation instructions for more information.
I have tried to create a software tool which makes implementing computer vision algorithms easy. You can even process images using the interactive Ruby shell. Under GNU/Linux it is already possible to write more sophisticated software such as a Webcam viewer on top of HornetsEye.