  (Abridged) We present a comparative analysis of the galaxy emission and QSO
absorption kinematics of a z~0.7450 MgII system and its candidate absorbing
galaxy (G5) located 3.86 arcsecs (28.3 h-1 kpc) from the QSO. We have obtained
a spectrum of the galaxy candidate, previously identified as a luminous edge-on
disk, and detect the [OII] 3727 A doublet at a systemic redshift of z =0.7450.
  From slit spectroscopy of this galaxy, we find v_rot ~> 210 km/s, and
possibly as large as 350 km/s. Plotted on the same velocity scale, the systemic
redshift of the galaxy coincides with the center of the absorption system,
although the absorption components span more than 100 km/s in either direction.
However, once the sense of the rotation is taken into account, there is no
absorbing gas at the projected velocity of the disk rotation curve. This
implies incompatibility with a simple disk scenario. Moreover, a re-analysis of
archival HST data reveals that the galaxy is only 0.3 L*, considerably less
luminous than previously reported in the literature. Analysis of the absorption
lines shows evidence for superbubbles in the interstellar medium (ISM) of the
absorbing galaxy, based on the striking symmetry between components and large
MgI/MgII and MgI/FeII ratios, indicative of large densities. The large velocity
separations between line pairings, dv ~ 150 km/s indicates that these bubbles
may be powered by OB associations comparable to the largest observed at z=0 and
that the gas is probably enriched to at least 1/10 solar metallicity.
