I had this very same project to do and after many hours of work, found that there is a limit of 10 meters your avatar can move from a fixed point in space. This means you will have to script the prim to move down the runway while playing a walking in place animation, stop and do a pose, and then a walk back to your original point. The advice is correct in you must move the hip in the animation, and Poser uses the body position instead of the hip to walk along a set path in Poser. Was a really frustrating learning process. I would be interested in hearing how you get it to work if it's different from any of these suggested ways. Good Luck!