Originally posted by synapsestorm but it seems the only way to zoom in and out with the 18-135mm lens is to do so manually.
That is correct. And AFAIK that is true of all modern dslr lenses, Pentax or otherwise. If I'm wrong on that I'm sure someone will be good enough to correct me.
Pentax did make "powerzoom" lenses at one time,
here is a link to one of them. However, the zoom function was a feature of the lens, not the camera. The "powerzoom" contacts that powered that feature of the lens are now used on modern digital cameras to power the SDM or HSM focusing motor and I do not believe the zoom feature will work on modern cameras.