The Yeast Washing Illustrated post tells you how to save and re-use yeast that you've already used once, though.
To culture yeast from a bottle, you need to make a very small batch of unhopped "beer" by just boiling some DME in water to get a starting gravity of around 1.030-1.040.
Search for "culturing yeast" or something similar and you should find instructions. Or click Wiki at the top of the page and search there.
Sierra Nevada yeast, by the way, is the same as WLP001/Wyeast 1056/Safale S-05. Probably has taken on some house characteristics by now (don't know how often they start their yeast culture over, if ever), but basically the same.