I think they have to be in midi format for both poly and mono (don't quote me though)
Anyway, here is a list of programs from download.com with ringtones as the search. I think the majority are free to try though
I'll never forget how lucky I was 7428 days, 11 hours, 16 minutes, 48 seconds ago
Ringtone Help - by LoochTheMan on 09-10-2004 at 08:54 PM RE: Ringtone Help - by .blade// on 09-10-2004 at 09:21 PM RE: Ringtone Help - by Vazza on 09-10-2004 at 09:30 PM RE: Ringtone Help - by Wabz on 09-10-2004 at 09:42 PM