Easiest way is to use Bridge w/ Photoshop creating a template. Open one image in photoshop, enter all the metadata you want, then press the button top right (the one that looks like a circle with a "play" icon inside) click "Save metadata template" name and hit save. Your template with all that info is now saved. You can either load the template into each image when open in photoshop. Or…to batch them all. Open Bridge. Select all applicable images, hit that play button at the top of your metadata view and click "append metadata" click your presaved template, and away you go. All metadata will be added.
Hope that helps.
-Kristen