Locate the "Line-In" jack on your computer tower. Most audio jacks are located in the rear, near the mouse and keyboard ports. Plug one end of the audio cable into the jack. If you do not have a specific jack labeled Line-In, plug the cable into your microphone jack.
Plug the other end of your cable to your cassette player's headphone jack. Rewind the cassette to the beginning or from the point you want to begin recording from.
Download a program such as Audacity to convert your cassette music to digital format. Audacity is free to download and is available for all operating systems. Other free programs may be available as well.
Start the program record feature and simultaneously start playing your cassette tape. The program has an audio level indicator to let you know when sound is being played. Stop the recorder when you are finished. Export and save the file as a WAV or MP3 file.
Start your CD burning program and add the audio file to the burn list. Burn the file to the CD and you will be able to listen to the audio in any CD player.