I have an update on this. I checked my outputted source and saw that the jquery file (gallery.js) was being loaded. I tried disabling plugins, changing themes.
Then I got serious. I put File Gallery on a local install of WordPress, used the stock Twenty Ten theme, zero plugins (except File Galley of course). The latest release of the plugin's Simple template was not loading the jquery file correctly I guess, because Default theme was still being used.
According to the documentation here, the Simple theme was available starting with version 1.6.4. So I downloaded every version of the plugin since 1.6.4.
I next replaced my Simple template folder with the deprecated versions from the top down to 1.6.4.
Only 1.6.4 shows the Simple template correctly. Most others show the Default template, except for version 220.127.116.11, which shows a partial Simple.
I don't know if this methodology is really sound or not, since the core of my File Gallery plugin is still at 18.104.22.168. Nevertheless, 1.6.4 Simple works as advertised!
Aesqe, any ideas why that is?