As opposed to MP3 and other lossy codecs, FLAC doesn't "throw away" any of the information in the music so it sounds better than standard MP3 files and is preferred by many audiophiles. The downside is larger files, but because FLAC files are compressed they're only about 1/4 of the size WAV files ripped directly from your CDs. Well, and there's also the fact that very few portable audio devices will play FLAC, but then you can always make MP3 files from your FLAC files. It's the best of both worlds in a way.
There are actually a large number of programs for Windows that will play FLAC files. You can find a list of them at the FLAC site.
http://flac.sourceforge.net/documentation_tasks.html#windowsYou can even make Windows Media Player play FLAC files, with a little effort.
http://www.xiph.org/dshowIn addition to the Direct Show filter I linked to at Xiph.org, you'll also want this extension for Windows Media Player that will read the FLAC metadata (song title, artist, etc.)
http://wmptagext.sourceforge.netHope that helps wildbill.