Free vehicles:

Use a text editor to edit all the files in the "data\cars" folder except "hai.dat" and "zf.dat". Change the first line to "0" in each of the files. All vehicles should now be free.

Change number of passengers:

Use a text editor to edit all the files in the "data\cars" folder except "hai.dat" and "zf.dat". Change number in the second line in each of the files (except for the cars) to set the number of passengers that can enter.

Mission select:

Place the pointer over the "Options" button at the accident screen, but do not click the mouse. Type sixteen to display the mission selection menu.

65.000 Money:

Open an Savegame with an Hex-Editor, look for the Offsets 44 und 45 and overwrite the Offsets to FF FF.