How do i change my screen's resolution to the desired number instead of the preset?

How can i get my computer's screen resolution, on windows XP to, a resolution that's somewhere BETWEEN 800x600 pixels and 1024x768 pixels?How do i change my screen's resolution to the desired number instead of the preset?
control panel %26gt; appearance and themes %26gt; under ';pick a task'; #4 change screen resolution