Geithner talked about this in his book and basically said that they wanted to do something for Lehman but couldn't and only after that collapse was everyone aware of how serious the situation was and the rules changed. The Fed was operating in no man's land and didn't have the authority to do what it needed to do. This is pretty clear in hindsight with the huge AIG lawsuit. They stretched the rules for AIG because they were staring into the abyss.