File compression programs like Zip and Arj and Rar offer password protection options. They're not terribly secure, but they'll slow down anyone who doesn't know about (or can't be bothered with) obtaining a zip-cracker.
Tony, that's almost exactly what I was looking for. It is a little bit cumbersome exiting the file, verifying that I want to update the archive and delete the temporary file, but it's just a couple of extra mouse clicks. The [lack of] ultimate security is appropriate to the value and sensitivity of the data.
Now I just have to find and delete the original (unzipped) files in my backups and the recycle bin.
Thanks!
tanstaafl.