You can only get what Square gave you with that game. Unless there's some unofficial patch I know nothing about. Anyway, 640x480 was quite acceptable when FF8 PC was released. You can find it as annoying as you want, but people still worship ol' Privateer - 320x200 256 colours or something.

On another note, I doubt FSAA was even a daydream when FF8 was made. Asking to have support for it NOW looks... silly in my eyes. Live with it, it's not like it's important.