Hanging a new museum show is never less than a complicated job. Getting all that art positioned just so--it's a test of nerves. But when the show is for Richard Serra, whose typical work is made from coiling steel plates that weigh 20 tons or so, complicated doesn't begin to describe it. Putting the things in place is like moving a dozen rockets to their launch pads. There's one sizable new Serra, called Sequence, that consists of 12 plates weighing a total of 243 tons. The average commercial airliner weighs 199.