I have a Pentax Zx-50 camera with a Pentax FA 28-90mm lens, and I am looking into purchasing a 80-200 manual focus lens and a Pentax k1000 camera. I would like to know if the lens that I already have will fit on the Pentax K1000 camera that I will buy and vice versa. <!--color-->
Yes; I have both of those cameras. The great thing about Pentax is their backward, forward compatability. Their lens from the 60's will work with their new digital cameras
The AF body is, I think, one of those with the "crippled" K mount, so you might need to make sure your Pentax lens is an "A" series or later one. The K1000 will be happy with all Pentax lenses that have an aperture ring, only exluding the DA digital-only lenses and the FA-J series that have no ring. Compatibility is excellent generally, but not 100% so for all bodies with all lenses.