I have found and used a nice little application to edit sounds and make ringtones. It’s called WavePad Sound Editor.
A full featured professional audio editor for Windows or Mac OS X. It lets you make and edit music, voice and other audio recordings. When editing audio files you can cut, copy and paste parts of recordings and, if required, add effects like echo, amplification and noise reduction. WavePad works as a wav editor or mp3 editor but it also supports a number of other file formats including vox, gsm, real audio, au, aif, flac, ogg and more.
Here is a link to the site.