Hmm...in the Official FF8pc Configurator (the one that came with that game, aka FF8config ver1.0), it lists "Paletted Textures" as one of the features it looks for...
..yes, that's the same "Paletted Textures" feature that FF7's config looks for, and the same one that needed to be bypassed for nVidia cards running FF7....and here we are, noticing the nVidia cards seem to not take doing the FF8 world map well....
It's a shot in the dark, but perhaps the world map uses more paletted textures than the rest of the game, and nVidia drivers aren't as fast in supporting it?
Again, the only evidence I have that would point to this, would be nVidia not really caring about having Paletted Texture support in its drivers (hence the need for the test bypass in the FF7 config), and may have done a "half-assed" (pardon my french) job in coding for that support.
On a side note, I used to run FF7 on an old Trident 2mb 2D-only card, before I got that V3 2000 PCI that I've used for so long.... the only test the Trident card would pass was, ironically, "8-bit Paletted Textures". I wouldn't be surprised if your 2mb card had the same test results.
On the other hand, it could have been that the card had an uber-fast DirectDraw driver (assuming you had to play it in Software Rendering).