From Interfluidity, a good explanation of what really happened in the Fed-Bear Stearns-JP Morgan deal:
http://www.interfluidity.com/posts/1207251546.shtml
The only thing I’d add is that the U.S. Treasury is actually the counterparty of last resort because it has guaranteed any losses from the deal up to $29 billion. So, the Fed is the counterparty of next-to-last resort. Hmmm.