The native Video BIOS resolutions can be determined by following these steps:
VBE version 3.0 0x112: Direct Color, 640x480x32 0x101: Packed pixel, 640x480x8 0x111: Direct Color, 640x480x16
The meaning of these codes is also explained here.
Translating these codes into their Linux equivalents by add 0x200 to them yields the following values:
Hexadecimal Decimal 0x312 786 0x301 769 0x111 785
The linux kernel source code documentation file Documentation/svga.txt explains that these codes can be used by the kernel at boot time to select the screen resolution. For example, grub's /boot/grub/menu.lst might be modified by adding vga=769.
title Debian GNU/Linux, kernel 2.6.22-3-686 root (hd0,0) kernel /boot/vmlinuz-2.6.22-3-686 root=/dev/sda1 ro vga=769 initrd /boot/initrd.img-2.6.22-3-686
The first generation Eee PC's have an LCD screen with a native resolution of 800×480. If the operating system outputs a different resolution, the screen will either go blank, show only a part of the output, or compress/stretch the output to fit the screen. In the case where Linux is putting out 640×480, it will be stretched horizontally. When looking at console text, such as is often visible before the X Windows system is running, the text will appear slightly wider than normal and will be blurred by the video hardware in order to stretch it.
So how can the Video BIOS be updated to the native resolution of the screen? There is no VESA code number which denotes a 800×480 screen. Therefore we have to update the Video BIOS using a tool such as 915resolution.
Adding Video BIOS Resolutions in bootloader
For using 800×480 resolution at boottime Nathan Coulson wrote a 915 hack patch for Grub2 bootloader.
Very important: Messing with bootloader you can get your system to unbootable state. More important is that Grub2 config syntax differs from Grub legacy (used in Xandros) so you have to update config files also or system doesn't boot! (though you can still boot it manually from Grub commandline).
Trying install Grub2 when you are under unionfs you probaply just get your system also to unbootable state. (Howto remove unionfs)