In Photoshop CS and earlier versions we were able to duplicate a mask by using the following steps:

Duplicate Mask CS- make the layer that needs a duplicate of a mask the active layer (it will now have a double border).

- drag/drop the mask (A) that you want to duplicate to the New Layer Mask icon at the bottom of the layers palette.

  

  

  

  

  

  

Things have changed in Photoshop CS2 and we’re now unable to use this method, because Photoshop CS2 doesn’t allow us to drop a mask on the New Layer Mask icon. The new method to duplicate a mask in Photoshop Cs2:

Duplicate Mask CS

- Hold down the Alt key (Option key on the Mac) and drag/drop the mask (B) you want to duplicate to the proper layer (it doesn’t matter which layer is the active layer).