We report on the magnetic and transport properties of thin films of La0.67Ca0.33MnO3 as a function of annealing temperature, substrate material and film thickness. The films were sputtered from a stoichiometric target with the same nominal composition and were grown epitaxially on SrTiO3 and LaAlO3 substrates. We find a clear correlation between the ferromagnetic ordering temperature TM and the magnitude of the magnetoresistance ratio (MR ratio). Also, TM appears to be extremely sensitive to the preparation conditions: within the one composition investigated, TM could be made to vary between 125 K and 255 K.