the easiest way to get ringtones is through iTunes, and i don't mean buying them through iTunes. what you want to do is take the section of song you want and make it about 30secs long. import to iTunes and convert to acc. once the file is acc just change the file extension from acc to m4r and drag it into you ringtones section. sync your phone and your ringtone will be there.
to convert to acc the file needs to be in iTunes. when you are in iTunes right click the file and select convert to acc. to change the file extension i just googled file extension changer and downloaded a program for that.