Plopbox looks like a great idea, shame it doesn't work in Opera.
If you want MP3s (or aac,wav,amr,8svx,aiff,vorbis,flac etc.) converted from Mods (or IT,XM,S3M and a whole bunch of MIDI formats) using only your browser then give
Media Convert a try, it's not perfect but it does the job and even gives you a WAP link once it's finished for some retro-ringtone action.