yakitori2009

There are many ways to create m4r format ringtones for iPhone.
Free software like iRinger or iTools can also make ringtones easily.
http://www.iringer.net/
http://www.itools.cn/index.htm

Provided you have the song on hand, just cut your favorite portion within 40 seconds.
Finally you can use either iTunes or iTools and import them to your iPhone.

Using iTools to import / export ringtones can be done easily.
You can also use iTools build in function to download songs and make ringtones.
Give it a try and I am sure your will like it.