Humanity and Sinfulness
Introduction to Biblical Anthropology (MP3)
Original Sin I (Covers imputed sin from Adam, the an outline of Pelagianism)
Original Sin II (Continues discussion covering Augustianism, Semi-pelagianism, Arminianism)
The following lectures go into the same material in somewhat greater detail, and are based on the Westminster Confession of Faith. Please note these lectures were recorded in 1987, and the audio quality is less than wonderful.