Some of the information for this game requires the "Keys To The City" downloadable content. It can be obtained by using the following steps.
Play on Xbox Live with someone who has "Keys to the City" and ask to play it. When he quits, go to the main menu within five minutes, then select "Keys to the City".
Log into the Xbox Live Marketplace. Do a search for "Crackdown". Find the "Free For All" download and the "Keys To The City" will be in there, for free.