  We present a scheme for entangling two micromechanical oscillators. The
scheme exploits the quantum effects of radiation pressure and it is based on a
novel application of entanglement swapping, where standard optical measurements
are used to generate purely mechanical entanglement. The scheme is presented by
first solving the general problem of entanglement swapping between arbitrary
bipartite Gaussian states, for which simple input-output formulas are provided.
