This study will last up to 24 months for mothers and their children. Participants will be stratified based on their CD4 count at screening. Women with CD4 counts of 200 cells/mm3 or more will be in one of two treatment groups and will be randomly assigned to receive either TZV twice daily or LPV/RTV and 3TC/ZDV twice daily. Once in labor, treatment group participants will continue to take their assigned HAART regimen and will also be given additional ZDV. Women with CD4 counts less than 200 cells/mm3 will receive nevirapine (NVP) once daily for the first 14 days, then twice daily, and 3TC/ZDV twice daily; these women will be in the observational group.