I'm going to have to agree with SarahB. I've been using Inventor since the days of Release 1 and i aquired that my freshman year. I had no clue what it was, so I instaled it on my computer and started playing. Through TechnoKats I got a later version, and then i enrolled in the Project Lead The Way course at my school last year. Because of my experience with just messing with Inventor I was way ahead of everyone in the class, and now I consider myself pretty proficient with the program. Heck I'm even modeling a "hog roaster" for a kid that goes to a county school (I guess it's his senior project).
Start off by playing with the program, play around with the settings (turn on "edit dimension when created" or something to that effect), and then try out the tutorials or even grab a pair of calipers or something and model something around your house. It can be anything from an ink pen, to a floppy disk, etc..
Have Fun!
