  The recent development of numerical schemes for Relativistic MHD (RMHD)
allows us to model the acceleration and outflow properties of winds from
compact sources. Theoretical models suggest that acceleration and collimation
of the flow are extremely inefficient when the speed is close to $c$, in
contrast with many observations. Numerical results for an axisymmetric rotator,
both in the case of monopolar and dipolar magnetic field will be presented,
suggesting that in ideal RMHD acceleration is indeed inefficient. I will also
mention numerical challenges and stability problems of present simulations.
Finally I will discuss the interaction of a pulsar wind with the surrounding
SNR. I will present emission maps based on numerical simulations of the flow
inside the nebula and how they can be used in comparison with observations to
derive informations about the properties of pulsar winds far away from the
source.
