Download Fluke, a small Mac OS X utility that allows you to play FLAC files in iTunes, from http://blowintopieces.com/fluke. With Fluke, you don't have to convert your music files.
Restart iTunes on your computer after you download Fluke.
Right-click on the FLAC file you want to listen to using iTunes. Go to "Open With," and then "Other." Enter "Fluke" into the search bar to locate it.
Click on "Fluke," then click on "Open" to open the application.
Click "Yes" when a pop-up window appears asking if you want to import the FLAC file into iTunes. Your music file will now then be entered into the iTunes application and you will be able to play your music from within iTunes.
To play the FLAC file you just added, open iTunes and click on the song.