To transfer old audio lectures from cassette tape to MP3 format, use a line level adapting cable to connect the tape recorder's speaker output to the computer's line input. Recording software, including free options like Audacity, can be used to capture the audio. Start recording while playing the tape, adjusting the playback volume for optimal sound quality. It’s advisable to record shorter segments instead of full-length lectures to avoid large file sizes. If a line input is unavailable, USB adapters can connect via the earphone jack. For Windows users, the built-in sound recorder can be utilized, but it has a 60-second limit per recording. To extend recording time, repeatedly hit record after each 60 seconds. The resulting WAV files can be converted to MP3 using audio conversion software to save space.