ADPCM codecs have been included since Win95, so any Windows transcoder that uses ACM should be able to do the job.

Hi,<BR><BR>I've got a 4-bit WAV that's resisting my attempts to decode. I've tried uLAW, aLAW, and VOX ADPCM without luck. I've also tried to open it with the proprietary X-Box ADPCM and Dreamcast CDI ...

This paper presents the Adaptive Differential Pulse Code Modulation (ADPCM) method of digitally storing and reproducing speech or other waveforms. A detailed explanation of the encoding steps is given ...