I would be satisfied if your generator could:
1) Find my HFS & it's setting from my machine (reg or ini)
- If it can't find it from the defaut location then of course ask
2) Find out (from the settings file) what VFS file I use currently
3) Close HFS (to save any possible changes to the current VFS)
4) Load that VFS into generator
5) Allow me to simply select which folders I'd like to have the gallery for (and optionally their subfolders)
6) Generate images & edit the VFS respectively (apply Diff Template for the gallery folders)
7) Save VFS and load it to HFS again
...This way it might be easy enough even for novice.
I'm not sure about the (6), if it's the best way to do things...just the first idea that came to me. It means that the generator would also have those .tpl files matching HFS's templates. These *.gallery.tpl's would have only the [files] section (and maybe [styles]) edited to display thumb gallery. This way ToG, Terayon and the default template could all have their own editable gallery.tpl files which would then be set as the Diff Template for the gallery folders. Hope you understand what I'm trying to say
I think there also should be an option to save the thumb either to the folder where the original images are OR to HFS's program folder. Personally I hate if something (like some image viewers) create index files or something like that to my image folder thus destroying folder dates & times.