> Option "UseInternalAGPGART" "no" #used to be yes
I would have set it to yes myself; I assume it was causing trouble.
> as you can see, i've already removed all modelines except for the 1280x960 modeline, ...
What happens if you comment out all of the modelines?
> Depth 24
Not that is should affect your screen resolution, but 16 bit is the optimal depth for 3d-acceleration with OpenGL.
Does this line:
Appear in your config? If all else fails, try adding it.