Using the full, three-dimensional potential of galaxy cluster halos (drawn from an N-body simulation of the current, most favored cosmology), the distribution of the X-ray-emitting gas is found by assuming a polytropic equation of state and hydrostatic equilibrium with constraints from conservation of energy and pressure balance at the cluster boundary. The resulting properties of the gas for these simulated redshift zero clusters (the temperature distribution, mass-temperature and luminosity-temperature relations, and the gas fraction) are compared with observations in the X-ray of nearby clusters. The observed properties are reproduced only under the assumption that substantial energy injection from nongravitational sources has occurred. Our model does not specify the source, but star formation and active galactic nuclei (AGNs) may be capable of providing this energy, which amounts to (3-5) × 10^-5 of the rest mass in stars (assuming 10% of the gas initially in the cluster forms stars). With the method described here, it is possible to generate realistic X-ray and Sunyaev-Zel'dovich cluster maps and catalogs from N-body simulations with the distributions of internal halo properties (and their trends with mass, location, and time) taken into account.