The International Phonetic Alphabet (IPA) is not a language but a set of agreed special symbols for describing the pronunciation of any language. Within Unicode they are spread over a number of different blocks, and your OS X should be able to display them if you install the fonts Charis SIL or Doulos SIL. The Wikipedia IPA page is a good way to test your fonts, as the charts there are available both as text and as images.
To input IPA you need to use the Character Palette or a special keyboard, such as that created by SIL or linguiste.org. Any modern word processor should work, but not Word X or AppleWorks.
On my iDisk you can find a "fun" keyboard which maps various IPA characters to the normal English letters to produce a form of upside-down text. It's the top item named xxxlpxuxnx.keylayout.