  We discuss the entanglement properties of bipartite states with Gaussian
Wigner functions. Separability and the positivity of the partial transpose are
characterized in terms of the covariance matrix of the state, and it is shown
that for systems composed of a single oscillator for Alice and an arbitrary
number for Bob, positivity of the partial transpose implies separability.
However, this implications fails with two oscillators on each side, as we show
by a five parameter family of explicit counterexamples.
