You need to realize that some people get sponsorship requests all the time and don't have time to read through everyones. So get to the point right away. Something along the lines of... "Hey I'm a 15 year old skier out of (fill in location). In 2010 I got 1st place in (fill in comps). Please check out my edit at vimeo.com/(fill in the blank).
Thanks for your time.
Sincerely, YOUR NAME
The same thing goes for your edit. Don't make a 5 minute edit with a 1 minute intro that doesn't have skiing. Get to the point, show your banger shots.
Realizing not everyone wants to compete but is still worthy of sponsorship, then just send the link to your edit.
After you cover the important stuff at the beginning of your email, you can feel free to throw in some other stuff like a short bio on yourself, photos, other sponsors, plans for the up coming season, how the company will benefit from sponsoring you.
There is probably something I am missing, but I hope this helps.
Good Luck with your resume