Primary: To determine whether combination vaccination, i.e., priming with a vaccinia recombinant-containing HIV envelope (HIVAC-1e) followed by boosting with a recombinant subunit envelope protein (gp160 or gp120), provides enhanced immunogenicity compared to subunit vaccination with the individual recombinant envelope proteins only. To compare the relative immunogenicity of a panel of HIV envelope subunit vaccines when administered as boosters following recombinant HIV-vaccinia priming. To evaluate the relative immunogenicity of one versus two doses of recombinant HIV-vaccinia prior to the subunit protein boost.