If you always do a mission for the mafia when they are available eventually you will get to the mission "gimme my money". When you go on the mission kick the silver box that is sitting there by the black box you have to retrieve and walk over the minature silver boxs that will appear where the big silver box was. They will have a green circle around them there will be two or three boxes. Each one will give you money they will dissapear when you walk over them and you will see your money acount get more money and you will here the sound that you here when you collect money.