I got a copy of inventor from a camp I went to (the college that hosted it was upgrading, so they gave all of their copies to the participants in the camp) and couldn't for the life of me figure out how to use it for building 3ds for roller coasters. In my version, everything was being made on the centimeter scale, rather than meters, so it was much too small for easy use, so I don't use it anymore.
Now I use the free, unregistered object creator to make simple stations and other things for my rides. It is extremely limited, and even more so since I don't know how to make custom textures
I'm hoping to get Maya and/or 3ds Max for christmas this year, as well as Photoshop, and then I'll be able to pwn. Hopefully. Btw, Maya, in case you didn't know, is a professional modeling program used mainly for animations, but can make some really cool-looking things. I was looking around and found a student license for both Maya and 3dsMax for $275.95. It includes both programs. With luck my parents will decide not to be cheapskates this year lol.[:D]