You need to connect the Minidisc Player to your computer with a suitable cable, play the tracks and record the audio on your computer as it plays (ie you press 'play' on your Minidisc player and 'record' on your pc, just like record to tape or whatever back in the day). You can use the built-in Windows sound recorder but it's not too good apparantly. There's a program called something like Music MAtch Jukebox which I believe is recommended for this kind of thing.
In fact
here's the MausicMAtch Jukebox homepage. I accept no liability if it turns out to be less than perfect, but it seems to have a good reputation and it's free!
edit: ha ha, and
here's a site that seems to be in uncanny agreement with me.