Specify vga mode in /boot/grub/menu.lst

            640x480   800x600   1024x768   1280x1024   1600x1200   Ask user at boot
8 bits    vga=769   vga=771    vga=773     vga=775       vga=796      vga=ask
16 bits  vga=785   vga=788    vga=791     vga=794       vga=798      vga=ask
32 bits  vga=786   vga=789    vga=792     vga=795        vga=799     vga=ask

e.g. kernel /boot/vmlinuz-2.6.24-23-generic root=UUID=9e4bb76f-afcb-415c-b529-c9305f6a6c6d ro quiet splash vga=794