As soon as you get it, let us know, Autodesk is offering a reward for turning in software pirates of their software .
Seriously, a professional engineering forum is not the place to ask how to get "free" copies of the software many of us (or our employers) have paid large sums of money to use.
If you are indeed a student, I'm sure Autodesk has a program for educational institutions, contact them directly, or through your instructors.
Above is a link to the new Inventor LT page. Its free to download the main differences between it and the full version is that it does not allow 3D assembly and sheet metal design. However it can be used to learn the user interface and core modeling technics used in Inventor.