frame size is width * height * color depth in bits
dunno about Pixar but the latest batman sources had frames in the 200MB range
rendering farms do not need or often even have video cards, just the master or in many cases not even that, its all done remotely........the data is sent to the farm and eventually a video file(s) is pumped out, the farm splits it up into smaller chunks then does it mostly in parallel.........racks of clustered machines with mucho processing horsepower and RAM
the workstations at the design end will have top end graphics cards often using openGL and they split up the tasks there over several boxes too, some will do composting, file management, work flow management etc etc
wanna see what is really involved on a slightly smaller scale, look up "elephants dream" and download the movie and sources, they used mostly open source software and then borrowed a mainframe from a state college to do the final render which took a few months
