I've heard of a race that goes for 1000 or 2000 miles. I don't know what it's called but i'm pretty sure it's raced with atv's. Does anybody know what it is or it even exists?

 

http://www.score-international.com/
http://www.bitd.com/
http://www.off-road.com/

SCORE has a Baja 250, 500, and 1000. And, they had a 2000 in the year 2000.

And, Best In The Desert, has the Vegas to Reno race (about 500 miles), plus several shorter races.

Check the archives at off-road.com, they usually have good race coverage for all these events.