Russell Brown just released something for CS5 that should do the trick for you.
http://russellbrown.com/scripts.html See the Adobe Watermark Panel for CS5. An older version for CS4 is down a bit on the page. The Watermark Creator Version
This script looks like it would definatly work for me but I am not a NAPP member so I can't download it. Any ideas?
I may be telling secrets, but it is the installer for the new panel that is CS5 only. If you download the CS5 version and manually install it in CS4 it does work.
Extract Adobe Watermark.jsx, Adobe Watermark.swf, and the two png files to the plug-ins/panels folder where Photoshop is installed and restart Photoshop if it's open.
Well I tried downloading the CS4 version and it didn't require a password afterall (just says it does on the site). Thanks for pointing me to the write place this is working great.