I prepared a public repository on GitHub with all the code of the crystal window decoration, from crystal-0.5 for KDE-3.2 to the current crystal-2.2.0 for KDE-4.9 beta.
Please feel free to contribute:
There are also ongoing discussions about integrating the crystal window decoration into the official KDE SC, moving all development into the offical KWin tree, next to the current default Oxygen deco.
Currently all major distributions ship optional binary crystal packages. If not, see the official crystal project page on kde-look.org.