Two- and three-dimensional MHD simulations are used to provide a theoretical description of 2 wire molybdenum X-pinch experiments. The initial evolution from solid wires to the formation of supersonic jets and a central micro-Z pinch is found to result from the slow rate of wire ablation and from the distribution of the Lorentz force. The growth of m=0 instabilities triggers the formation of micron sized regions of intense x-ray emission with plasma pressures in the Gbar range. A simple analytical model is used to predict how the maximum density and temperature scale with material and current.