Not only can you not do it officially, but you cannot do it legally, morally,
or (for most people) technically.
iTunes and song-sharing services like it (Rhapsody, for example) provide
tunes for your listening pleasure, not for you to republish in some other
format.
Anybody moderately competent with computer audio could tell you where you
could find free software to capture the audio as it is playing and then save
it to an MP3 file you could insert in your PowerPoint.
Anybody moderately moral would not share that information in a public forum
where it would encourage song-stealing copyright violations.
As you might tell from my monicker, I've involved in music and a strong
supporter of copyright enforcement.