  Using numerical simulations of galactic disks resolving scales from ~1 to
several hundred pc, we investigate dynamical properties of the multiphase ISM
with turbulence driven by star formation feedback. We focus on HII region
effects by applying intense heating in dense, self-gravitating regions. Our
models are two-dimensional radial-vertical slices through the disk, and include
sheared background rotation, vertical stratification, heating and cooling to
yield temperatures T~10-10^4K, and thermal conduction. We separately vary the
gas surface density Sigma, the stellar volume density rho_*, and the local
angular rotation rate Omega to explore environmental dependencies, and analyze
the steady-state properties of each model. Among other statistics, we evaluate
turbulent amplitudes, virial ratios, Toomre Q parameters including turbulence,
and the mass fractions at different densities. We find that the dense gas
(n>100 cm^-3) has turbulence levels similar to observed GMCs and virial ratios
~1-2. The Toomre Q parameter in dense gas reaches near unity, demonstrating
self-regulation via turbulent feedback. We also test how the star formation
rate Sigma_SFR depends on Sigma, rho_*, and Omega. Under the assumption that
the star formation rate is proportional to the mass at densities above n_th
divided by the free-fall time at that threshold, we find that Sigma_SFR varies
as Sigma^(1+p) with 1+p ~ 1.2-1.4 when n_th=10^2 or 10^3 cm^-3, consistent with
observations. Estimated star formation rates based on large-scale properties
(the orbital time, the Jeans time, or the free-fall time at the
vertically-averaged density) however depart from rates computed using the dense
gas mass, indicating that resolving the ISM structure in galactic disks at
scales <<H is necessary for accurate predictions of the star formation rate.
