We provide the general tadpole conditions for a class of supersymmetric
orientifold models by studing the general properties of the elements included
in the orientifold group. In this talk, we concentrate on orientifold models of
the type T6/ZM×ZN.Comment: 8 pages, 1 figure, Latex2e. Proceedings of RTN Workshop on the
Quantum Structure of Space-time and the Geometric Nature of Fundamental
Interactions and EXT Workshop on Fundamental Interactions and the Structure
of Spacetime, Kolymbari, Crete, Greece, 5-10 Sep 200