  Galaxy cluster peculiar velocities can be inferred from high-sensitivity,
high-resolution multiple-frequency observations in the 30 to 400 GHz range.
While galaxy cluster counts and power spectra are sensitive to the growth
factor, peculiar velocities are sensitive to the time-derivative of the growth
factor and are hence complementary. Using linear perturbation theory, we
forecast constraints on Omega(matter), the Hubble constant today, and the
dark-energy equation of state parameter, given 820 densely sampled cluster
locations (near redshift 1) from a Lambda-CDM N-body simulation and 820
sparsely sampled cluster locations in a broader redshift range.
