Edit your player file (.PLR file) and add the following
lines to the [GAMEOPTIONS] section:
The Medical and Safety cars are just two bonus cars you can
drive, they do not function as medical/safety/pace cars in
the game. In fact, the cars are pretty lame looking and do not
handle or perform anything like the real Mercedes-Benz vehicles
because they have been given the VEH file from an F1 car, they
don't even have a correct cockpit view.
The 2-seater is the training car from the "school" mode.
Theme Art is just some alternative background graphics for some
of the menu screens.
No great shakes here, you probably won't even notice the difference.
The 3 certificate levels are graduations from the 3 training
school phases (Indy, Monza, Suzuka).