Autodesk has training books just like SW. Inventor Essentials, Part Modeling, Etc. I would check eBay and see if you could find some. Mine are pretty old back at release 2 of the software and wouldn't help you much.
With 7 yrs of using SW, I don't think you'd have much trouble learing IV at all
I'd been using IV for about 10 yrs before swiitching to SW about 4 yrs ago. Without attdending any training class, I spent a week of playing with SW and went thtu. the tutotial which is available with both sofrwares and I was about 60% productive right at the 2nd week. Same as what I did with IV, the forum is the best place to learn thing. I learn millions things from this forum for the lat 4 yrs - Nothing can compare of to the learning experiece I have from here.
Just a warning - at the beginning (from my experiece), there are somre frustrations because what you think is simple in SW or IV but kinkd of awkward for another sofware - but after couple months, these problems will go away
If you get the AutoDesk Inventor Essentials book for your version you pretty much can't go wrong. I was priveledged enough to take the Inventor class at our local technical college with one of the three authors, Alan Kalameja, several years ago and could understand why he was AutoDesk instructor of the year more than once. Unfortunately he passed away not too long ago, but most of his material is still relavant and in the books up through 2012 version. Co-Authors Daniel Banach and Travis Jones were both very good as well and most of the book is very easy to follow with good examples and tutorials. If you are an avid SolidWorks user, you should pick it up pretty easily.