  The DEEP2 survey has now completed half of its planned three-year lifespan,
and we have collected approximately 50% of the data, putting us exactly on
schedule. The survey plan calls for spectroscopic coverage by July of 2005 of
\~60,000 galaxies over 3.5 square degrees to a limiting magnitude of
R_{AB}=24.1; the great majority of these objects are at 0.7<z<1.4. We describe
here one method by which DEEP2 can set constraints on the equation of state
parameter of the Dark Energy, w. By counting the number of virialized groups
and clusters we find in redshift space as a function of their redshift and
internal velocity dispersion, we probe both the volume element and the growth
of structure at z~1, each of which depends on w. Studies of early DEEP2 data
indicate that the method is likely to work, and preliminary indications are
that a total of ~250 small groups will be counted in the full survey, leading
to a constraint \delta w ~ 0.1 if combined with both the velocity dispersion
distribution of z~0 clusters from the Sloan Digital Sky Survey and an
independent measurement of \sigma_8. We also provide a general description of
the DEEP2 observations and target selection, including the algorithm by which
galaxies are placed on slitmasks, to provide context for discussion of DEEP2
cluster samples.
