  We generalize W*-superrigidity results about Bernoulli actions of rigid
groups to general mixing Gaussian actions. We thus obtain the following: If
\Gamma\ is any ICC group which is w-rigid (i.e. it contains an infinite normal
subgroup with the relative property (T)) then any mixing Gaussian action
\sigma\ of \Gamma\ is W*-superrigid. More precisely, if \rho\ is another free
ergodic action of a group \Lambda\ such that the crossed-product von Neumann
algebras associated with \rho\ and \sigma\ are isomorphic, then \Lambda\ and
\Gamma\ are isomorphic, and the actions \rho\ and \sigma\ are conjugate. We
prove a similar statement whenever \Gamma\ is a non-amenable ICC product of two
infinite groups.
