Can I use iTunes with my FLAC files?

iTunes does not play FLAC files.

However, certain applications are available that enable you to listen to FLAC files through iTunes.

These include Fluke for Mac.
Alternatively, VLC and Songbird are players that can both be used to play Flac Files on Mac and PC.
Alternatively you can convert your FLAC files to wav, aiff or mp3 in order to play them in iTunes.