  Starting with configurations of fourbranes, fivebranes, sixbranes and
orientifolds in Type IIA string theory we derive via M-theory the curves
solving N=2 supersymmetric gauge theories with gauge groups SO(N) and Sp(2N).
We also obtain new curves describing theories with product gauge groups. A
crucial role in the discussion is played by the interaction of the orientifolds
with the NS-fivebranes.
