The purpose of this research study is to compare how the body reacts to different strengths of an experimental cell culture-grown whole virus A/H5N1 flu vaccine when given with or without the addition of aluminum hydroxide adjuvant. Researchers will also look at how much antibody is made to the influenza virus hemagglutinin (HA) after subjects receive the H5N1 vaccine. Three hundred healthy adults aged 18-40 years will participate for approximately 9 months, which includes screening. Participants will receive 2 doses of vaccine or placebo injected 28 days apart. Participants will have blood samples taken up to 7 times and have 8 scheduled study visits.