Autodesk inventor

I need help with the Robotics 2010 Design Challenges, it says I can get a free version of Autodesk® Inventor® but I would like to know the details that if anyone knows: does it charge the professor? can I get an access code from a professor that isn’t mine? Is the free version just the trial? And if there are any other details that you think I should know let me know please.
Thank you

Edit: oh am I able to use Google sketchup Instead?