http://www.minidisc.org is probably the best site for all things MiniDisc.
Be warned that some current units have notable bugs, and of course the units themselves are filled with Sony's DRM limitations. For example, MP3s cannot be dragged and dropped on the units. They must go through SonicStage (their software for managing your stuff on the MiniDisc and Hi-MD (1GB MiniDisc).
Some notable issues so far:
http://forums.minidisc.org/index.php?showtopic=10434 Titling error (missing alphabet characters on US model)
http://forums.minidisc.org/index.php?showtopic=10304 Sony deliberately rolling-off the frequency response of mp3 playback to make their own ATRAC encoding sound superior.
- many other DRM limitations preventing uploads & downlaods the way you might expect them to go (smoothly and without fuss).
If you are referring to a dedicated PC MiniDisc unit, they never took off. Sony did once release an MD Data drive. Some time ago.
MDs are really slow transfer devices for use on the PC, so unless you really need it for the size or durability of the discs themselves, I would avoid using them solely as a format to save data to (there are cheaper and faster alternatives like DVD-RAM, etc).