Don't let the website discourage you, but XLD (X Lossless Decoder) is really useful and powerful. It can convert pretty much any popular format.
Personally, I use it to convert .flac files to Apple Lossless Format (no loss of quality by going from one to another, in case anyone was wondering).
Apple Lossless is (obviously) supported natively in iTunes, whereas .flac is not (natively).