Crisis Coverage: Why AIG?

It appears the Fed has bailed out AIG with an $85 billion loan and an 80% stake in the company plus a bunch of other provisions like replacing management. This is good news in that the feared crisis is back on hold for now.  But why did they save Bear, Fannie/Freddie and AIG, but not Lehman?  AIG is an insurance company and not an investment bank right?  As usual, the true nature of what happened is a bit murkier.