You can make a PNG watermark in Photoshop and use that in Lightroom.
The watermark would have exactly the same text everywhere, though, not something specific to each photo, except the filename.
You can Google for Lightroom School Proof Watermark to find various discussions. Here is one: http://www.lightroomforums.net/threads/creating-a-school-portrait-proof-sheet-with-a-singl e-image-and-text.23118/
This tool is probably exactly what you need as it will use different metadata for each photo. It says Lightroom 2 but the documentation says it works for Lightroom 2 and above.