Download and install Audacity. This is a free audio editing program that will allow you to convert your old cassette tapes to MP3s. It is compatible with both Macs and PCs. You can download Audacity at audacity.sourceforge.net.
Open Audacity, go to the "Edit" menu and click on "Preferences." When inside the "Preferences" menu, change the channels so they are set to 2.
Click on the "File Formats" tab. Then click the "Find Library" button and navigate to the folder on your hard drive containing the lame_enc.dll file. This will configure Audacity to use the LAME MP3 Encoder. If you don't have the Lame MP3 Encoder, you can download it for free at audacity.sourceforge.net/help/faq?s=install&item=lame-mp3.
Choose a bit rate for your recordings. For audiotapes, a rate of 128Kbps is recommended and 256Kbps is adequate for music.
Plug one end of your audio cable into the headphones jack on your tape player and plug the other end into the "Audio In" port on your computer.
Make sure your tape is rewound all the way to the beginning.
Press "Record" on Audacity and then press "Play" on your tape player. Your tape is now being recorded onto Audacity.
Separate the songs once one side of your tape has finished recording. You do this by highlighting a section of the recording and saving it is a separate file. You will be able to tell where each song starts and ends because of the few seconds of flat line that will be displayed on the sound-wave graph. Save each selection as an MP3 and name it whatever you want.