There is a completely free train simulator called BVE, which stands for 'Boso View Express". Originally Japanese based it has become very popular and there are now many routes and trains from all over the World.
A good website for those interested is TrainSimCentral at
http://www.trainsimcentral.co.uk
There are three versions: the basic one is BVE2, more complex BVE4 and now an Open BVE for developers.
I run BVE2 on my computer, but it is limited to cabviews and forward movement. The signalling systems are however very realistic and the train simulation, speed, braking, acceleration, adhesion and so forth quite excellent.