Hi There,
Check out this website (
http://bxd.autodesk.com/). It's really a great tool for beginners as it does a good job in laying out the basics. The inventor videos start about half way through if you're not interested in Fusion.
Just a word of caution; Inventor, like anything, takes practice. The key thing is to stick with it. Your first time, it might take you a matter of days to put together your first DT. Your second time, it might take a matter of hours.
A second word of caution; A lot of parts, and I mean A LOT OF PARTS are available online. Check out some of the online places (3D content central, KOP libraries, etc.) or the particular vendor (AndyMark, VEX, McMaster, etc.)
Hope this helps,
- Sunny G.