Doesn’t work with DRM material, but to create a ringtone, do a Get-Info on the song and click on the Options tab. Then add a start/stop time and convert it to AAC (Advanced Menu -> Create AAC Version). Next, save the file to your desktop, remove it from iTunes and change the extension from .m4a to .m4r. Now drag it into your Library, click on the Ringtone list and you can use it right away.