Thanks to Download Squad for pointing me to Tag Scanner.
It's a Windows tool that lets you update tag information for various kinds of audio and video files and to rename the files themselves, based on the tags.
I could have used this a couple of days ago, when I needed to rename some MP3s so that they played in the correct order on an MP3 CD player that didn't take notice of ID3 tags.
Of course, a small Ruby script sorted out that problem ... and provided a welcome distraction from my socio-babble assignment :-). However, not everyone's a hacker, so this looks like a useful tool.