  This talk summarizes results from recent MHD simulations of the role of a
dipole magnetic field in inducing large-scale structure in the line-driven
stellar winds of hot, luminous stars. Unlike previous fixed-field analyses, the
MHD simulations here take full account of the dynamical competition between the
field and the flow. A key result is that the overall degree to which the wind
is influenced by the field depends largely on a single, dimensionless `wind
magnetic confinement parameter', $\eta_\ast (= B_{eq}^2 R_{\ast}^2/\dot{M}
v_\infty$), which characterizes the ratio between magnetic field energy density
and kinetic energy density of the wind. For weak confinement, $\eta_\ast \le
1$, the field is fully opened by wind outflow, but nonetheless, for confinement
as small as $\eta_\ast=1/10$ it can have significant back-influence in
enhancing the density and reducing the flow speed near the magnetic equator.
For stronger confinement, $\eta_\ast > 1$, the magnetic field remains closed
over limited range of latitude and height above the equatorial surface, but
eventually is opened into nearly radial configuration at large radii. Within
the closed loops, the flow is channeled toward loop tops into shock collisions
that are strong enough to produce hard X-rays. Within the open field region,
the equatorial channeling leads to oblique shocks that are again strong enough
to produce X-rays and also lead to a thin, dense, slowly outflowing ``disk'' at
the magnetic equator.
