This tutorial takes you through mapping the model and applying textures.
Click on the picture to open the tutorial as a pdf file in a new window or right click to save it locally. The latest version is 1.06.
These tutorials are for v2.49b or v2.70 and up of Blender. I recommend though that you use the latest version.
Blender is a 3D editing program that can be used to make models of just about anything, it is free to use and the first tutorial details where to obtain the exporters needed for Trainz.