The scoring system is not listed (or at least I can't find it) on either the Miss Universe or Miss USA websites. But if you look at the individual state websites it will list the judging system used. The prelims still give an equal weight to all three levels of competition. I happened to the Missouri website and it explained it pretty easily.
http://www.missmissouriusa.com/2006pageantinfo.html
The judging system is going to be the same from the state level all the way up to Miss Universe b/c they are all the same company.