  We present results from two-dimensional numerical simulations of a supersonic
turbulent flow in the plane of the galactic disk, incorporating shear,
thresholded and discrete star formation (SF), self-gravity, rotation and
magnetic fields. A test of the model in the linear regime supports the results
of the linear theory of Elmegreen (1991). In the fully nonlinear turbulent
regime, while some results of the linear theory persist, new effects also
emerge. Some exclusively nonlinear effects are: a) Even though there is no
dynamo in 2D, the simulations are able to maintain or increase their net
magnetic energy in the presence of a seed uniform azimuthal component. b) A
well-defined power-law magnetic spectrum and an inverse magnetic cascade are
observed in the simulations, indicating full MHD turbulence. Thus, magnetic
field energy is generated in regions of SF and cascades up to the largest
scales. c) The field has a slight but noticeable tendency to be aligned with
density features. d) The magnetic field prevents HII regions from expanding
freely, as in the recent results of Slavin \& Cox (1993). e) A tendency to
exhibit {\it less} filamentary structures at stronger values of the uniform
component of the magnetic field is present in several magnetic runs. f) For
fiducial values of the parameters, the flow in general appears to be in rough
equipartition between magnetic and kinetic energy. There is no clear domination
of either the magnetic or the inertial forces. g) A median value of the
magnetic field strength within clouds is $\sim 12\mu$G, while for the
intercloud medium a value of $\sim 3\mu$G is found. Maximum contrasts of up to
a factor of $\sim 10$ are observed.
