When Wall Street woke up Monday morning, two more of its storied firms had fallen. Lehman Brothers (NYSE:LEH) , burdened by $60 billion in soured real-estate holdings, said it is filing for Chapter 11 bankruptcy after attempts to rescue the 158-year-old firm failed. Bank of America Corp. (NYSE:BAC) said it is snapping up Merrill Lynch & Co. Inc. (NYSE:MER) in a $50 billion all-stock transaction. And the world's largest insurance company, American International Group Inc.(NYSE:AIG), was forced into a restructuring as it sought a lifeline from the Federal Reserve