This study will determine which of four doses of GW873140 can safely be given to adults to lower the amount of virus (HIV-1) in the body. GW873140 is a new type of anti-HIV drug called a CCR5 receptor antagonist. CCR5 is a receptor on T cells (a type of white blood cell) where HIV-1 enters and then infects the cell. GW873140 is intended to block the CCR5 receptor so that HIV-1 cannot enter the cell.