We present results from recent simulations of the formation and evolution of clusters of galaxies in a LambdaCDM cosmology. These simulations contain our most physically complete input physics to date including radiative cooling, star formation that transforms rapidly cooling material into aggregate star particles and we also model the thermal feedback from resulting supernovae in the star particles. We use an adaptive mesh refinement (AMR) Eulerian hydrodynamics scheme to obtain very high spatial resolution (~ 2 kpc) in a computational volume 256 Mpc on a side with mass resolution for dark matter and star particles of ~ 10^8 M_solar. We examine in detail the appearance and evolution of the core region of our simulated clusters.