We will be in Hong Kong for one week. Do we need a visa to visit a few places on the Mainland?

How do we get the visa if it's necessary? Do we get a one-entry, or multiple entry? If we want to go to one place on one day, then back to Hong Kong, then to another place another day, then back to Hong Kong, WHICH VISA DO WE APPLY FOR, HOW DO WE GET IT TO A PERSON IN LOS ANGELES WHO WOULD TAKE IT TO THE CHINESE EMBASSY, AND HOW DO WE ULTIMATELY RECEIVE THE VISA BY 25 JANUARY 2012 FOR OUR TRIP TO HONG KONG?????????????????????