Ron Hoffman over at Gadgetronicx has written up an article on his DIY model train controller project:
Model trains are fun toys which every one of us used to play with in our childhood. Many sophisticated and attractive model trains are available in the market now a days yet the basic principle in build a controller for it remains the same. I built a Model train controller which is equipped with Acceleration and deceleration control using the PWM technique. And also Forward reverse button to control the direction.
Project details at Gadgetronicx project page.