In your bootloader, LILO or GRUB, add a line in the top section, above the choices, that says vga=ask . It will then pause and ask what res you want. It will also give you a key to hit to get a choice. Pick one and see how you like it. After you decide which you want to use all the time, you can change the vga=ask to vga=### with the correct numers to signify which res you want. It tells you what they are when it gives you the list of choices.
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