Cannot get 1280x800 screen res in Foresight on Mac

Currently, I have Ubuntu Hardy, Sidux 2008-1 and Foresight 2.0.2 on my MacBook. In the first two, I have 1280x800 screen resolution without having done anything special. Indeed, the /etc/X11/xorg.conf file contains no modelines in the display subsection.
This post and this will describe what I did and didn't do.
I have tried everything I could think of, including adding

Modes "1280x800@60"

, but everything leads to a 1024x768 resolution.
Indeed, even if I go to Systems>Admin>Display and change the resolution to 800x600, it still stays at 1024x768.
very strange.