The Fed isn't spending any money (yet). The Fed allows commercial banks to borrow money (directly from the discount window, when they're in trouble). Now, for the first time, the Fed is allowing investment banks to borrow money the same way commerical banks do. (Whether or not that's a good idea, only time will tell.)
Because of the credit crunch and the lack of confidence in the markets right now, the Fed acted to help ease those problems.
This has the potential of being costly though, if it doesn’t succeed. After all, the collateral for this borrowing are those $30 billion dollars mortgage-backed securities, which don't look very good right now.