The reason that only one PC is being used is because the output file is AVI. If you want multiple computers rendering at the same time on the same scene, you need to render TARGAS. When the output is set to targas, each PC will render a frame and save the image with a number attached to it. Once you have scene rendered, go into Premiere or whatever post-production program you use and import one of the targas with "Numbered Stills" checked. The program will automatically put together the rest of the targas..
Hope that helps.
