You would need the rendering executables and everything needed to run it on each node. You will never get a 500 PC network to operate like one computer, so your post about not wanting them to do whole frames each would require the rendering distribution program to cut them up in pieces (which several of them can do, but less effective than doing whole frames). As for actually logistically installing Maya on 500 computers together with the client for whatever netrender app you choose is something I'd not want to do without getting paid. And if I remember correctly Maya is shipping with unlimited render licenses for its software renderer, however only one MentalRay render license per copy. Good luck.