However the above does not support the file format normally used by FLAC files (think of the file format as the Envelope, and the FLAC compressed music as the letter inside that envelope).
This page describes an additional plugin which may solve this for you.
http://barelyfocused.net/blog/2006/10/12/native-flac-in-itunesquicktime/
However, while FLAC is lossless, is fairly widely supported (except without a great deal of effort in iTunes and on iPod) and produces files that are a bit smaller than other lossless formats, I feel it is too much hard work for very little extra benefit. I would instead suggest you use Apple Lossless which works with all the following (some times admittedly with additional plugins).
iTunes (of course)
iPod (of course)
Apple TV (of course)
iPhone
Windows Media Player (yes really!)
Media Center (yes really!)
Xbox 360 Media Extender (yes really!)
Roku Soundbridge
SlimDevices Squeezebox
Sonos ZonePlayer
Foobar 2000
WinAmp
dbPowerAmp
VLC
MPlayer