I did this once, some years ago: used the cord with plugs on both ends that I had at home, got a walkman tape player (it was some years ago), plugged in the headphone jack of the tape player and the microphone jack of the computer, and used Sound Recorder (yes, Sound Recorder) to record the audio and then convert to MP3.
It was quite an adventure: I actually had ten tapes with many parts of audio on it that I wanted to save separately, so recorded the part that I wanted, paused the tape, and saved and converted the file, then repeated for the next part.
Probably nowadays there is better technology out there that doesn't require using Sound Recorder and all the pausing and converting. But hey, this was over five years ago. I had a *tape* walkman, for goodness sakes!
I actually was very happy with the result at the end, considering all the work I went through.
malu
