Mlsoft - I don't think Greenspan could have done much. After his "irrational exuberance" speech, the Market recovered quickly. If he had given another, the same thing would have happened. By the third or fourth time, people would have ignored him.
He could have tried raising interest rates, but all the Kudlidiots of the world would have screamed to high heaven, and he quite likely would have been outvoted in the OMC.
Even if he'd been able to raise rates and choke off the bubble, he'd know that he would forever be blamed as the person who killed the greatest bull market of all time. The ensuing downside would have all been "his fault".
Sometimes, these things just are too strong, and they have to play themselves out. I'm not blaming anyone for it.