The only way to animate a horse is with a motion capture file. The Forge sells .bvh files for horses at www.the-forge.ie. Credo Interactive also sells .bvh files and poser horse models at www.charactermotion.com. This is their animania section. They have a more complete set and includes walking. However, I think most of the motion capture files have the horse going in a straight line rather than following a path.