First set up your D80. You will need to change the USB interface from M to PTP (Picture transfer protocol). Its is in the menu settings. Then plug your D80 to the USB port on your Mac.
Next, open the Automator application, its the little robot icon in your application folder. Select "Image Capture" from the list on the left then drag "Take Picture" from the second column to the third column.
Dont bother with the settings, as you are only going to do this once per session.
Click the play button, the D80 should snap a picture and the file will be stored in whatever folder you specified. Or the Picture folder if you did not specify anything.
Here is the interesting thing, after pressing play in Automator, the interface between your camera and your Mac are now open. If you click on the shutter yourself, the picture you take will be imported into the Pictures folder.