The article gives some detailed examples of how the guarantee will work that goes beyond what the Treasury described. It's important to note that the program only guarantees the money you had in a MMF on 9/19/2008. It's also important to note that the program is only temporary. Treasury will review the program after the initial 3 months and will decide if it should be extended until 9/19/2009.
Make sure you don't confuse money market funds with money market accounts. A money market account is basically the same as a savings account which is FDIC-insured and offered by banks. A money market fund is a mutual fund holding a collection of short-term debt investments, and it is not FDIC insured.