Um you can install software on your Treo 680 and play MP3s as ringtones directly. No conversion required, or just use Garageband to snip the MP3 to the part you want to play. Copy it to your SD card, and use the program to play that MP3 as your ringtone.
Home: 2006.5 iMac 20"
Me: 2010 MacBook Pro 13", iPad Mini Wifi 32GB Black, iPhone 4 16GB Black
Wife: 2011 MacBook Air 11.6", iPhone 4 16GB White
Are you backed up??? If so, why? Psyllium Fibre is not free but will do wonders!