And now for a word from an orphan in the creation world, an program that used to be included with Trainz for free - GMax. The baby brother of the professional 3d Studio, it is a simpler 3d modelling program that is easy to use and is still good for making backgrounds and distant buildings and when wrapped in Trainz Asset Creation Studio, exports IM files directly for Trainz. If you add some bump mapped textures, they can look pretty good too. It's still freely available around the Internet.
If you have ambitions of eventually making more sophisticated objects, I would skip GMax and go for more modern programs.