8.04, iBook G3, 640mb
I can't get higher than 800x600x60hz, and with this laptop it just uses the upper left corner, with the rest of the display repeating parts of the main display.
I've added "Modes "1024x768" " to the xorg.conf and it just breaks the gui altogether... "Screen init failed".
I'm betting it's needing a specific driver (Rage Mobility 128 I think). I tried "ati" and "r128" but I may be putting them under the wrong section.