There are two parts to this study. In Part A, participants will be sequentially assigned to one of three groups. Each group will receive injections of different amounts of either DNA vaccine or placebo at entry, Month 1, and Month 2. This is followed by identical injections of glycoprotein/adjuvant or placebo at Months 6 and 9. Group 1 will receive 250 mcg each of the gag and env DNA plasmid with microparticle vaccine; Group 2 will receive 500 mcg of each vaccine; Group 3 will receive 1000 mcg of each vaccine. Participants will be enrolled sequentially from low to high dose beginning with Group 1.