blender planks revisited

Hi guys, this is an issue that I already thought closed, but it has returned with a vengeance … so I re-open it in a new thread; it is an issue with the planks game exercise (http://www.youtube.com/watch?v=iK7E0jfvTIM); the problem is that the structure of planks I create becomes unstable when I apply physics to it; the planks don’t rest on the ground, but they jitter for a while; when the jitters of all the structure are added up, the result is like an earthquake with planks tumbling down

In the previous post I was advised to play with the physics steps and that worked, but not totally: when I put a seven stories structure up, the whole thing shakes; it seems there was still vibration, though very reduced. I am totally unable to build a structure that can resist the force of physics!!

Can anybody help?

Any ideas, anyone? I am totally at a loss. Thanks in advance guys.