Fixed.
- Get Info on a song, set a Start - End range in the song for the part you want as a ringtone
- Set the exporter to AAC
- Right-Click : "Create AAC Version"
- Right-Click the new 30 second song - "Show in Finder".
- Copy it to desktop
- Delete if from iTunes and from the disk (not your copy on the desktop).
- Get Info on the original song, remove the Start and End range.
Go to the desktop and :
- Rename the 30 second song, changing its extension from m4a to m4r.
- Import into iTunes.
Congratulations on your free ringtone.