A comprehensive model of the excitation and kinematics of cometary molecules has been developed and used to analyze data obtained on comet Levy (1990c). This work builds on previous studies to develop models of the excitation and distribution of HCN and H$\sb2$CO in the coma and to apply these models to comet Levy in order to determine the physical parameters of the cometary coma and test models of the possible origin of H$\sb2$CO in comets. The collisional cross sections as a function of $\Delta$J have been considered in the excitation models for both molecules, based on quantum mechanical calculations. The vectorial model has been adopted for consideration of possible daughter species and a Monte Carlo calculation technique has been applied to develop both parent and daughter molecule models for H$\sb2$CO so that we can calculate its production rate and discuss its original source. With the high quality of spectra for both HCN and H$\sb2$CO molecules in comet Levy, we are able to use our models to constrain their abundance and some physical parameters of the coma. These new observational results confirm that microwave spectroscopy is an efficient tool to study cometary parent molecules, and help us understand the formation of our solar system.