This. The second post has the instructions for this.You can also just use iTunes. It's not difficult to make 'em yourself once you get the hang of it.
ooohhh yeah. tried it out and it worked out for meI did a write up about this, here is the link. http://hubpages.com/hub/How-To-Customize-iPhone-Ringtones
You need a garageband to do this.