Thank you for your help. The metadata added by Spotlight is not written into the file itself, so it isn't what I'm looking for. I know iPhoto and iTunes, but I was wondering if there is a tool that supports editing metadata (that is stored within the file) in multiple formats (pics, music, video, docs, etc.).
It's always better if the metadata goes with the file, when you send the file or copy it, and it's stored in a standard way that many programs on different platforms support (like XMP).