I've been wanting to do this forever and am finally going to do it this week.
It took me forever to find a set of plans or anything other then someone just tying a rope around their car tire with a pulley on the other side.
http://books.google.com/books?id=D9kDAAAAMBAJ&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false (Page 225) This took me forever to find, but i figured there'd be something in Popular Mechanics, and i was right!
I'm going to be doing this same setup using a 5hp lawnmower engine.
I know this might interest some of the more technical side of NS. Also didn't know where to post, i thought i'd get the most legit responses here.
What i'm going to when it snows, go hike up by Red Lakes (tahoe) and set up 2-3 powder jumps and a couple rails with my friends and we're going to lap them. I'm so stoked. Sooooo stoked.