The TB will let you set any mp3 as a ringtone. It has the ability to clip the song to the length you want it.
I use "EarCatch Ringtone Express" on my computer to create ringtones from mp3 files. You can try it out and decide whether to purchase. It gives you a lot of control over clipping/splicing from an existing file, various save modes, fade in/out controls, etc. Very easy to use. I have some more complicted programs to modify tunes, but this is simple and to the point for making your own ringtones - or just modifying music files for your own enjoyment...