oliver :
is generating temporary .wav files a practicable alternative for you ?
then you could use "system" from the motex library to do an mp3->wav conversion with some command line utility like "lame" and load it into a buffer for variable speed playback. after use you can delete that temporary wav file within PD too (with a dos command to "system").
of course this isn't a really cool solution, and there is a time lag for the converion stuff
Yeah it isn't cool at all, but propably I'll end up doing something like this. First I thought about converting all the mp3 files to wav, but your idea seems to be better. On the other hand, I don't know if calling some external command line tool while pd is processing audio, won't cause any audio dropouts/clicks/etc. I want to fit pd, sound & graphic files on to my 512MB portable USB memory, and using .wav as sound file format makes it somewhat impossible (due to a number and size of these files). Also a friend of mine asked me if I could build for him a mp3 "dj mixing" patch (something like NativeInstruments Traktor). Well, I think I'm going to try your solution for now.
Anyway, thanks for suggestions.
cheers, Bart