OK, as far as I know, as long as you have run Steam and Railworks on that PC (laptop) before, and fire up Windows with no Internet, when Steam loads, it will tell you there is no Internet connection, and do you want to continue in off line mode.
And once you've done that, you might want to change Steam settings so it either always starts in offline more or it automatically logs you in when you start it, which lets in run online or offline without you needing to make any other changes to the settings.
