I have a PC. (Gateway) This is how I cut music.
1) When in Itunes, you probably need to convert the file format to something that Audacity will recognize. Depending one how your Itunes is formatted you can do it the way MimiG said. Right click on the song title and convert it. Though I can't seem to convert to mp3, I convert to AIFF format.
**If when you right click you don't see anything about AIFF format, go to Edit>>Preferences>>Import settings>>Import using, choose AIFF encoder. Then right click on the song title again, and this time it should say convert to AIFF.**
2) Go to Audacity, click open and import the AIFF version.
3) Make your cuts. Save your project.
4) When finished, go to file, and export to either AIFF or WAV. **If neither of those options are there, you need to format Audacity as well.** Go to Edit>>Preferences>>File Format>>AIFF/WAV (which ever you choose) Go back to file and export in whatever format you chose.
5) Go back to Itunes, File>>Add File to Library and find your edited version to import back into Itunes. Save it to a playlist and then burn to CD.