Why do you say that Mike? It might be too much for stock electric railroad power but you could use a higher voltage/current capable transformer to deliver plenty of power, granted you start to run some moderate risk of electrocution or fire if something shorts the tracks out. I doubt you'll find anything off the shelf for this kind of thing though.
In order to determine if it's feasible or not you need to get a working boiler using a gas setup FIRST, once you have a working gas powered boiler it's simple, determine the wattage that the flame is producing and value the power supply and heating element to match that. With the scale you're working on you're not going to need a huge amount of heat though so a small pencil torch would probably work fine, unless you're in a REALLY enclosed space the gas setup might actually be safer than an electric one.
One problem you may have with such a small boiler though is that as engines like that get smaller they get faster as well, and the pitch they produce changes. So while you might be going for the authenticity of steam power the sound and feel of a miniaturized steam engine is going to be nothing like a large sized setup. If you want authentic sounding setup stick with electric drive a good sound effects system and the fake steam like Mike suggested.
Just as an example, imagine the whistle of a train, if you were to make one to scale and push air through it you'd get a tone so high you'll irritate nearby dogs =) The same thing will happen to the noises the engine makes.