In the past I have already addressed this issue by publishing guides on how to make a desktop based on KDE but VERY VERY similar to Mac OS X.
Of course required to carry out 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, like Ubuntu for example, while not function on the KDE desktop environment, such as Ubuntu.
The most interesting aspect is that this package will not only deals with changing the desktop and windows to catch the style of the apple, but also several external programs such as Firefox, Thunderbird, and Rhythmbox.
The result is quite good: