Well, after the seemingly bad situation yesterday, there's good news. First, I installed SuSE on VMWare to try it out, some. While there is no formal definition of the encoding of filenames (which are just null-terminated character arrays), common usage dictates that they be interpreted as UTF-8 (the Linux GUIs and some terminals do this). That means it would be moderately safe to translate Unicode filenames (and by that I mean UCS-2) to UTF-8 on Linux (and possibly POSIX at large).
Next, I was mistaken about the behavior of Windows NT on non-Unicode-capable drives. It does indeed appear to use UTF-8 encoding for filenames on such drives. The reason I thought it didn't was that it was appearing as unprintable characters (boxes, to be specific) in Explorer on the computer I tried it on (which was not my computer). Apparently it's been so long since I've used such a thing that I'd forgotten that Windows XP doesn't come with Asian fonts...
Lastly, while I could support (with effort) both the Unicode and ANSI versions of Windows file API functions, it's much easier to just use the Unicode version, and leave Win9x support (which doesn't support the Unicode versions) to the Microsoft Layer for Unicode.
So, in the end it looks like it will work fine to use all Unicode for filenames in LibQ.
On an unrelated note, I went and picked up the Hitachi 250 GB hard drive for $50 at Fry's Electronics. While I was in the checkout aisle, a couple of other things caught my eye, as well: the Quick Study Japanese Grammar and Latin Vocabulary sheets. So, I picked up those, as well.