Men's small will definitely be a tad long on you for most snowboard pants. You could probably get away with ski pants, though.
I hate to say it, but you might have to rock some fat-kid snowboard pants!
Go to the young men's section and see if they have anything that fits. Some brands (like Foursquare) do have pant length adjustments, but you'll still have a pretty baggy fit at 5'3"