open your image make a new layer by going to layers " new layer" click on the T tool and pick a font and font size your happy type your logo... then goto the layers pallette and change the opacity to what ever suits ... go back to the layers and click merge down
your done... now if you goto the actions pallette and right click at he top of the pallette and pick new action and do all the above you will have a instant water marking tool ... shout if you get stuck

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