A few things to check out
http://team1323.com/cad/index.html
and assuming you acquired your autodesk software via students.autodesk.com and the FRC promotion check out this link
http://students.autodesk.com/?nd=kitofparts_view - autodesk provides much of the Kit of Parts in inventor files, you can download individual pieces or sets such as chassis sets
Also check out
http://www.3dcontentcentral.com/ they have lots of manufacturer designed parts to download in multiple formats. Additionally sometimes McMastercarr has 3d drawings. When you click on the specific part you want (I chose a random screw) it may have a 3d drawing on the side.
Feel free to skype me if you have some questions, I can try to answer them though I haven't used Inventor for a while