With the P80, I'm not aware of any UW housings for it. I thought I remember seeing one listed on Ikelite's page, but it's not there anymore.
Zoom is "bad" underwater since you want to get as close to your subject as possible. Zoom just makes it too easy to stay farther back and just zoom in. This results in colors being filtered out by all the water separating the camera from the subject.
Also, the long zooms make it difficult to use underwater add on lenses (at least wide angle ones) becasue the lens ports of the housings are so long (to accomodate the zoom range of the camera's lens) that you end up with the add on lens too far from the end of the camera's lens resulting in vigntetting (dark corners) at wider settings.
IMO for UW use, the ideal zoom for an compact digital camera is about 4x or less. If you want to stick with Nikon, I'd suggest you take a look at the P5100 instead. It's about the same price as the P80, it has 3.5x optical zoom (ther is also a telephoto conversion lens that that you can add on for topside shots to bring it out to 10.5x), it has a hot shoe for using manually triggered strobes, there are more housing options for it (Fantasea for about $200, Ikelite for about $450 and Fisheye for about $750) and people have been getting some great results with it.
