In one aspect, the invention provides methods and compositions for the expression of small RNA molecules within a cell using a retroviral vector. The methods can be used to express double stranded RNA complexes. Small interfering RNA (siRNA) can be expressed using the methods of the invention within a cell, that interfere with a viral life cycle by down regulating either the viral genome, a viral genome transcript, or a host cell that. In another aspect the invention provides methods for treating patients having suffering from infection, particularly infection with HIV.