Windows 7 64-bit will actually support 256 cores, according to Microsoft
. Whether a particular application will use all those cores is something that you will have to investigate. But note that you can only have two physical processors, so your proposed system would not work.
Several 3D programs, Carrara is an example, allow the rendering process to be spread aver several machines meaning there is no real limit to the number of cores that could be dedicated to the task. Another possibility would be to write software that uses the processing power of GPUs to do the rendering work using something like NVidia's CUDA; I'm not aware that any commercial software does this.