Yep, get Audacity (it's free, use google to find it).
Or one of many website that will convert and crop ringtones for you. I can't remember the one i recommended a few days ago on here. Let me see.
I've moving this over to the Media Section of this forum... lots of ringtone info there.
**EDIT: Try this for online OTA conversion and cutting.
Make Own Ringtone - Free MP3 Ringtone Maker