Its a bit of a stretch to say the Ancient Greeks could have built and used steam trains. Yes, they could use steam power, and yes, they could build rudimentary steam turbines, but none of these things was practical to use to power a vehicle. To do that, you would need a steam piston engine, and even if the greeks had had a blueprint, its unlikely that they would have manage the level of precision engineering and dye-making to build one that wouldnt explode. Also, even if they did manage to build one, its doubtful they had access to enough coal to keep it running for any significant amount of time.