Participants receive an injection (shot) of the DNA vaccine or a placebo (solution that does not contain any vaccine, medicine, or drugs) the day they enter the study and again at study weeks 4 and 8. They receive a booster injection of the rAd vaccine or placebo at week 24. The DNA vaccines are given with a needle-less injection device called the "Biojector 2000(Registered Trademark)" and the rAd vaccine is given using a needle and syringe. All shots are given in the upper arm muscle, alternating right and left arms with each injection. Patients fill out a diary card at home for 5 days after each vaccination, recording their temperature and any symptoms. The cards are turned in to the clinic at the first visit after all 5 days are completed. Patients must call a study nurse 1 or 2 days after each of the four injections and again 7 or 8 days after each of the first three injections.