There are two ways to implement Mac L&F on Windows. The first consists of modifying the main L&F class to return true when the isSupportedLookAndFeel is called. This is against the Swing/JDK license agreement, though.
Another way is to use a 3rd party Mac look & feel. Check out the website in the related URLs section for more information. Remember that you can dynamically load a look and feel without having to modify a properties file.