In the past I have already addressed The argument publishing guides on how to make a desktop based on KDE but VERY VERY similar to Mac OS X.
Certainly required to perform different operations and take care of the various aspects individually.
Today I propose instead a complete package: Phoenix: Mac4Lin ver.1.0 Released! .
Unfortunately it is only available for the GNOME desktop environment such as Ubuntu, for example, and does not run on KDE desktop, as Kubuntu.
The appearance more interesting is that this package will not only deals with changing the desktop and windows to resume the style of the apple, but also various external programs such as Firefox, Thunderbird, and Rhythmbox.
The result is quite good: