My action essentially resizes the photo to 640 pixels on the long side, creates a watermark, positions the watermark, sets the file copyright info, flattens and sharpens the image, saves the file to a folder called 'temp' on my desktop, and closes the file.
Michael is right, you don't have to have the images open to batch process them, but you do have to have a 'save as' command in the action, unless you want to go through and save each one, but for my purposes this is fine. It does work on horizontal and vertical images, which means you can just run it on an entire folder.
Anyway, I have made a generic version of my action, which you are all welcome to use. Just change the text to suit you, and change the file info to so that the copyright has your details in it (currently just says "your company here").
You can download it here:
http://www.swimminginafishbowl.net/PSAction/
Then go to your actions palette and load the action.
Cheers
Edit: If you don't have my font, which you probably don't, I'm not sure how it will look, so you may have to change that too.