Oh, and especially the people who think perspective-drawing is difficult, please read on, because this application takes care of that problem.
Infact, you might understand more about perspective-drawing if you actually work with "real" 3d-objects for a while.
Well, there is a complete Free application called "Blender" that is of extremely high quality and you can produce the same kind of results as you would with software costing $1000+
Just look at this gallery:
Blender Gallery
Is 3d-modeling in general difficult?
Actually, not really!
The common method is, like often with drawing, that you start from a primitive shape, like a cube (instead of a square when drawing) and then continue adding rough forms by deforming the cube in various ways and "extruding" "limbs" out of it if necessary and so on..
However, if you download this program and just try to "model" something, you most likely get nowhere at all. It's an absolute must to go through the basic tutorials carefully to understand how things work, otherwise you will just think everything is impossible and get frustrated.
Also, one thing to add about "Blender" is that the User interface might seem "strange" in the beginning. As it has been developed by a certain kind of people, they have decided that the most effective way of working is for the modeler to constantly have one hand on the keyboard ('a', 's', 'd', 'f') to be able to access modifiers quickly, instead of using the mouse to browse menus and clicking on tons of buttons.
Once learning this, modeling should go very rapidly.
Without further ramblings, download the software, go through some tutorials and see if you like the results you are getting.
Blender Homepage
Oh, and I attached a little picture that I did several years ago with another software to learn a bit how to model.
[attachmentid=667]
/Janne