Use a cassette player, play the cassette and connect the place where you plug in your headphone on the casette player with a 3.5mm audio cable. Like this:
The other ender of the 3.5mm audio cable connect to the line in/microphone plug of your computer. Use a sound recorder software to record the music when the cassette is playing. Recommend setting for music is mp3 2 channel 44100MHz CBR 192kbps.