The radio does not have a user code you can enter. If its in the car it was originally fitted to, it should just work. Each individual radio is registered on the canbus of the car its fitted to. This has to be done with the dealers diagnostic computer.
I also asked about the code card I dont have. The answer on this seems to be that insurance companies asked Fiat not to distribute key codes to owners, but to keep a central record, ( so all of them get nicked !!!! ), so if you need a replacement key , just go to your friendly Fiat dealer.