There is an easy way of enabling KWin’s composition capabilities even if you don’t have the possibility to run OpenGL. In fact, you can even activate composition within a virtual machine like VirtualBox.
Just right-click on a window title bar, choose “Configure Window Behaviour…”, click on “Desktop Effects”, mark the check box “Desktop Effects”, click on advanced options, and choose the “Compositing Type” XRender. Afterwards, most simple effects will just work, but effects like the cover flow window switcher, which require heavier OpenGL, might not work.
You can see more screenshots at Ivo Anjo’s blog post about it. Thanks for the hint, Ivo🙂