Breast-feeding has been shown to be very important for the physical and mental health of infants. This is especially true during the first 6 months of life. However, an HIV-positive mother can pass the virus on to her baby by breast-feeding. Because of this risk, HIV-positive mothers are encouraged to formula-feed, not breast-feed, their babies. In developing countries, however, some women cannot afford to formula-feed. If they do formula-feed, these women risk exposing their HIV status. These women have great need for methods that can lower the chance that they will pass HIV on to their babies. This study will test NVP as a way of doing this.