  We use imaging Fabry-Perot observations to explore the dynamical conditions
in four southern ultraluminous (L_IR > 10^12 L_sun) infrared galaxies. These
galaxies all show morphological and kinematic features indicative of a major
merger, but span a wide range of inferred dynamical ages: the youngest system
is just past the first encounter, while the oldest has already merged into a
single object. This diversity in dynamical states indicates that ultraluminous
activity is not confined solely to late-stage mergers. The Halpha emission is
more spatially concentrated in the later stage mergers, in agreement with
models which show that mergers drive gas inwards towards the nucleus, but high
luminosities are achieved even in young interactions where the Halpha is quite
extended. Our data indicate that physical details other than the dynamical
phase -- such as the internal structure or gas content of the galaxies -- can
play a strong role in determining the luminosity evolution of merging galaxies.
We also find evidence for massive star-forming complexes at large radius in the
tidal debris, reaffirming the notion that some dwarf galaxies may be spawned
during the merger of more massive disk galaxies.
