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:

http://www.amazon.com/Cables-Unlimited-AUD-1100-06-6-Feet-Stereo/dp/B000SE6IV8/ref=sr_1_sc_2?ie=UTF8&qid=1325316051&sr=8-2-spell

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.