GRUB allows you to choose the VGA definition it uses when booting. (Note: this does not affect the definition in Xorg).http://pierre.baudu.in/other/grub.vga.modes.html
You need to add the option vga=xxx on the kernel stanza in the file /boot/grub/menu.lst.
Of course, replace xxx with the video mode you want. Your kernel stanza will look like this:
kernel /boot/vmlinuz-2.6.18-6-686 root=/dev/sda7 ro vga=791
Here is a list of the available video modes:
| Colour depth | 640x480 | 800x600 | 1024x768 | 1280x1024 | 1400x1050 | 1600x1200 |
| 8 (256) | 769 | 771 | 773 | 775 | |
| 15 (32K) | 784 | 787 | 790 | 793 | |
| 16 (65K) | 785 | 788 | 791 | 794 | 834 | 884 |
| 24 (16M) | 786 | 789 | 792 | 795 | |
