I don’t know why I didn’t think to do more looking around before, but I’ve solved my wiki on a stick problem. Wikipedia has a comparison of wiki software, which includes a several that use flat-file databases.
Unfortunately, it’s not a true wiki on a stick. It will run on any Windows machine right from the thumb drive; the instructions there use Uniform Server, which runs Apache, MySQL, and PHP right from the thumb drive. DokuWiki is installed in the www directory there, so I can run it anywhere I’ve got XP (or maybe 2000) and a USB port.
As I mentioned in my previous post, MAMP won’t run anywhere but /Applications/MAMP. Mark made the good point that I could create a symlink from the thumb drive to that directory (or vice versa? you know what I mean), but by that time I already had DokuWiki working and didn’t feel like spending more time on it. As such, MAMP runs on my iBook with a local install of DokuWiki that points to the data directory within the aforementioned www directory. Voila, everyone uses the same data, and I am appeased.
It isn’t as flexible as I was hoping, but I’m really only planning on using it in three places: my iBook, my home PC, and on rare occasions when I need to make a quick note, my work PC. I can’t run it on other Macs without installing and configuring MAMP and DokuWiki there, but for my purposes, this setup will serve me well.