One more update, maybe it'll shed some light on the problem.
I mentioned at the end of the last post that the saved games weren't appearing. They just aren't in the Conquests\Saves folder. I loaded up Conquests once more, after rebooting, and this time the Korea saves I'd made weren't seen by Civ, either.
It looks like there's something messed up with creating and loading saves.
While browsing CFC, I found one more instance of this happening, on Page 11 of the Civ III Mac Technical Support. Here's a
link. It describes perfectly what was happening with me, only I had Vista instead of Mac OS 9.2.2.
The other possibility is it has something to do with my graphics card. I have an nVIDIA GeForceM 8600GT, with 256 MB of DDR2 RAM, on my laptop, and DirectX 10, along with the Vista-compatible-but-not-the-same-as-the-original version of DirectX 9 (Direct3D 9Ex?). The problem might be with that DirectX 10 is not backwards-compatible, and I'm not sure how Vista handles that with a DX10 card and DX9 applications. Not sure why that'd be causing issues with saved games, an Mp3 dll, or jgl.dll.
I'm still not sure what jgl.dll does - neither Google nor Jeeves gave me a quick answer. Chieftess mentioned something about it as, "the dreaded jiggle" in another post in Tech Support, though.
The other possibility is something with copy protection. When I tried to load CivIII on a Windows 98 VM within Vista it hanged on the splash screen, which according to CFC's CivIII Technical Issues FAQ indicates a copy-protection issue. This is the third machine I've installed Vanilla on, and second for Conquests, if that would cause an issue. Fourth and third if you count the native Vista install. But the Vista install did get past the splash screen with no problems.
Those are my three guesses as to the source of the problem. Thanks for any ideas/solutions.
Oh, and does anyone know if Mac CivIII Conquests can read saves made in the Windows version, based on .biq files made in the Windows Conquests editor? 'Cause I realized MacOS + MacCiv is cheaper than a full retail of Windows, though I'd have to check with Apple to see if I could run it without problems. Edit: Nope, has to be an Apple-labeled PC. Wonder if I can get Apple to label my PC? Y'know, get them to put a little Apple sticker on it.
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Edit: A complete re-install of the OS has Civ working again. Not sure what was wrong, possibly a driver? Whatever the case, I'm leaving the defaults on as much as reasonably possible to avoid re-triggering the problem.