Cool article on the previsualization of Clone Wars over on the Official Star Wars Blog.
What we’re working on is an extension of what George has been working on since the ’70s,” says Director Dave Filoni. "It’s really how do you cinematically tell the story. For George, telling a story starts and ends in editorial. ... George likes to edit and cut on motion and action, across head movements and hand movements. The editing of A New Hope is very fast paced. That kept the momentum moving in the story. He wanted to develop a way to get that final editing, which he could only do with live action coverage, really early on in the process."
Filoni explained how ILM’s Dennis Muren cracked this challenge in using videomatic techniques for the speeder bike chase in Return of the Jedi. Muren used tabletop models and action figures to cut together a rough version of the chase to give Lucas footage he could use in editorial. So before computers, they actually used these little models, and they got approximate camera angles. So you see the progress from static images to moving images.
We've used similar techniques in the past to mock up game levels and game play, so those techniques are useful when computers are around. Half the fun was to be discovered by unsuspecting hikers as they come around a bend in the marsh and find you and your team in the mud with action figures making pwew-pwew sounds!