According to http://www.minidisc.org/himd_mdcenter_news.html this is not possible:
All recorded audio is placed in a collection of ".hma" files (of unknown format) in a single directory on the MD. One large .hma file contains all the audio-data, the other files are for index-data & titles. These ".hma" files can be freely copied back to the PC hard drive, but no subsequent playback of them is possible. (They present fertile ground for further investigation however).
Gunther