1. Add the mp3 into iTunes.
2. Right click on mp3 and select "Get Info".
3. Select "Options" tab and adjust the time u want the song to start n stop, all within 40sec. Then press OK.
4. Then right click and select "Convert Selection to AAC".
5. After a new file has been created, go back to step 2 and unclick the 'start' and 'stop' options, then press OK.
6. Drag the new file out to your desktop. And delete the file in iTunes.
7. Change the filetype of the new file on the desktop from .m4a to .m4r
8. Doubleclick the newly named .m4r file and it will automatically be added onto your iTunes' ringtone folder.
9. Then just sync with your iPhone lor......

Anymore problem ah?

after you "right-click" convert ... you should see a new file right below your list..
click and drag that new file and drop it on your desktop/another folder where you can see the file extension ***.m4a . Delete this from the Itunes List

then rename that file that you drag out  to ***.m4r . (*just right click and rename it, don't need any software)
when you done rename .. it should warn you about changing the file type... if you do not get this warning means you didnt change the file type but instead u change the file name only.... **so make sure u change the file type
after that just double click and it will add into itunes automatically .. and then continue with the instruction