I am not an expert with Inventor, but have used it in the past; again not for v-belts specifically.
During my time with Baja we used the Tube/Pipe design accelerator. We also had to add our own tubing to the library that Inventor is pulling from. I am not sure exactly how we did it, but we were able to find some good tutorials online. Look for the YouTube ones as they typically walk you through it instead of just providing words to follow.
I was able to find a basic
help file that should help you get started.
I would assist in the looking of YouTube videos, but I can't view them from work. Please let me know if this helps.
Just curious, what are you designing that requires a v-belt?