How about the Pyramid Brewery (pyramidbrew.com) in Berkeley? According to the web page they can handle groups up to 200 people. They do have a fairly lage parking lot, but I doubt it would be big enough or empty enough for everyone to show off their great installs.

What we could do is adjourn to one of the UC Berkeley parking lots, which are usualy abandoned on weekends, especialy durring finals. They do charge $5 per car to park for the day, buf if we're all there with our cars you never know if they'll make us pay or call the cops to break it up. It's not a perfect solution, but parking is scarce in the bay area in general.