It's been a while since I tried this. I think you connect the headphone jack on you MD to the computer sound board. (line in or mic? I'd try line in first.) Then record the track with Microsoft's Sound Recorder. Open a new file, click "Record" on the software, and hit "Play" on MD for the track you want.
As you might expect, there are all sorts of settings on the Sound Recorder software that will prevent you from making a recording. You'll have to click your way through the menues to find them. At least some of the recorder settings you need are under the Edit--Audio Properties tab. Also, check your Play Control (the little speaker on the menu bar at the bottom of your screen), to make sure you haven't got your sound source turned off.
Many others have been through this. I just looked--at Minidisc.org and other places--and could not find a set of instructions for you. If you find a step-by-step guide on how to do it, please post the link here.