First you need to set it up to save in the format you want (using AIFF - which is uncompressed - is probably a good choice.)
1. Launch iTunes and choose Preferences... from the iTunes menu.
2. Click on the General tab (it should actually open in it by default!), and click the Import Settings... button
3. In the Import Settings dialog, choose the encoder you want to use from the Import Using menu. In this case, I'm using the AIFF Encoder.
4. Choose Custom... from the Setting menu. (if Custom is already chosen, then choose Automatic, and then choose Custom again to open the Custom dialog.)
5. Choose the Sample Rate, Sample Size and Channels; whether Stereo or Mono. I needed to match the settings from the camera video, which is 48 kHz, 16 bit.
6. If your audio is on an audio CD, just insert the CD and import the audio in the normal way.
7. If your audio file is on your computer (say an MP3 file) drag it in to iTunes. iTunes won't convert the file, but go find it in the music library, and right-click or Control key-click the audio track. From the pop-up menu, choose Create AIFF Version.
7. Now go to your iTunes music library in the Finder. You'll find both the original file, and the converted file: