How do I download other midi files as ringtones?

a) What extension must they have, in order to be recognized?
b) How do I "move" them from the flash card into memory, so that they appear in the ringtones list when I am chosing tones for calendar alerts and individuals' ringtones?

c) [and this is the most difficult one] does anyone know of a conversion utility that converts wave files to midi?

Thanks!