I'm sorry, unfortunately, the Nikon D80 does not have an actual "Date Stamp" function available in previous models. The only way to imprint the date/time is through the DPOF (Direct Print Order Form) function using a DPOF compatible printer (please see the information below from page 71 of your camera's manual). For whatever reason the Date stamp function has been discontinued by most newer camera makers. Again, sorry for the inconvenience. You will need to date photos with whatever photo software you are using.
I have done extensive research on this issue and found that there is really no logical technical reason that this function was eliminated, but all camera manufacturers have basically followed suit. Even Canon & Nikon's top pro cameras cannot put the date or time on the image file, only in direct print. Some Panasonic Lumix cameras and a couple low end Kodaks still have special modes that allow you to imprint the date. Exif (Exchangeable image file format) data (all info about the photo) is carried with the file and can be read by different photo programs and in windows by just right clicking on the file and selecting information.
Even though most people are unaware of the Exif data, it was a good excuse for camera companies to remove a convenience.
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