We consider configurations of Neveu-Schwarz fivebranes, Dirichlet four
branes and an orientifold sixplane in type IIA string theory. Upon lif
ting the configuration to M-theory and proposing a description of how
to include the effects of the orientifold sixplane we derive the curve
s describing the Coulomb branch of N = 2 gauge theories with orthogona
l and symplectic gauge groups, product gauge groups of the form circle
times(i) SU(k(i)) circle times SO(N) and circle times(i) SU(k(i)) cir
cle times Sp(N). We also propose new curves describing theories with u
nitary gauge groups and matter in the symmetric or antisymmetric repre
sentation. (C) 1998 Published by Elsevier Science B.V.