<qa>  How many studies will participants have during the study?Participants in this study will be randomized to receive either one of three different doses of vaccine or placebo. Participants will receive vaccinations or placebo at study entry and Months 1, 3, and 6. Both vaccinations and placebo are administered by intramuscular injection. Participants will be followed for 18 months and will have 12 study visits. Each study visit will include a physical exam, medical history, and blood and urine tests. Each participant will have four HIV tests during the study. Women will have at least five pregnancy tests during the study. 