There are many videos of Motocross crashes posted on YouTube. There is also a DVD compilation of Motocross crashes called Crash Kings Motocross, which can be purchased from amazon and many other online retailers.
All of the good ones !
The most obvious places would be sites like YouTube or there are many motocross sites online. Another resource for these videos would be social media sites, friends or favorite tracks could have some posted.
Arai, Shoei, and D1
there are many here are some: supercross arena cross motocross freestyle motocross indoor motocross outdoor motocross
Some good pi videos are "the pi song" "pi mnumonics", and more!
there is not good or bad injury in motocross if you get injured and you cant race then its a bad one but if you think you can manage to race then its good lol
On the Transworld Motocross website you can find - videos, photos, products, racing information and how to. You can also find pin-ups and updates. Feature stories are also available on the website.
Practise and practise. Push your self and you will get better and better and then you enter motocross races and if you are good you could get sponsored.
Honda CRF150R
it gives you a huge thrill
Moto-maniacs