Safe Neighborhoods Expansion Act of 2007 - Authorizes the Attorney General to expand the Project Safe Neighborhoods program to require each U.S. attorney to: (1) identify, investigate, and prosecute significant criminal street gangs operating within his or her district; (2) coordinate among federal, state, and local law enforcement agencies the identification, investigation, and prosecution of criminal street gangs; and (3) hire additional personnel to support the expansion of the program.