The Silicon Valley Mountain Bikers have made a horse-meets-bike video that is pretty good, and they also have a page of text on how to pass horses and how to pass hikers. How to pass: http://www.svmtb.org/about/a-mountain-bikers-guide-to-passing/
How to meet a horse: https://www.youtube.com/watch?v=Kh2lSRQqli4
