you don't necessarily have to cut the song down... you can click the icon to the left of the tempo and all, i believe, which is like two arrows in a revolving circle. "Turn on Cycle Region" is what it is.

Anyway, you can activate that and just target the part you want as a ringtone. (indicated by a gold bar above the waveform of the song). Then when u click Share>Send Ringtone to iTunes, it will only send that portion of the song.

Hope this helps, sorry it's kinda hard to explain. Hope you get the concept.