Make a ringtone...
1. iTunes prefs > General.
2. Click Import Settings… and set Import Using: to AAC Encoder.
3. Find the song you want and note the start/stop time you want the ring tone.
4. Right click - Get info, click the Options tab and set the start/stop times as above. (Note there is ~30-40 second max for ringtones)
5. Go to iTune menu File > Convert - Create AAC version. This creates a new file.
6. Drag this new file from the iTunes window to the desktop.
7. Delete the file from iTunes and also select Delete from hard drive.
8. On the desktop, rename the file whateveryouwant.m4r (first part you can change to whatever you want & change the extension to .m4r).
9. Drag the file back to the iTunes library at top left.
10. This new file will show up under Tones (at top left of iTunes).