The display supports a SXGA+ resolution of 1400x1050 pixels. I've spent a time trying to run the framebuffer at this resolution, but failed - now it runs at 1280x1024.

The grub setting for this resolution is just a

vga=775

so that the grub conf looks like this:

default 1
timeout 1

title=Gentoo kernel 2.6.4
root (hd0,0)
kernel /kernel-2.6.4-gentoo root=/dev/hda3 vga=775

title=Gentoo kernel 2.6.7
root (hd0,0)
kernel /kernel-2.6.7-gentoo root=/dev/hda3 vga=775