All participants will be followed for 15 months. Participants enrolled in Groups 1, 2, 3, and 4 will receive either the vaccine or placebo. Study visits will be completed at initial entry; five visits every 14 days for the first 2.5 months; and visits at Months 4, 4.5, 6, 6.5, 9, 9.5, 12, and 15. All participants will undergo physical exams, urine collection, and blood tests to assess safety, HIV infection, and immune responses to injections. Risk reduction/pregnancy prevention counseling will be given at every study visit. Participants will also be asked to complete questionnaires about outside testing and beliefs at certain visits.