You could manually set it within the gfx options.First make sure you have the latest drivers and stuff because it's a newer feature(for ati). control panel>display>settings tab>advanced should get you there.
Yeah make sure it's the entire catalyst package and not just the driver.The catalyst package is what includes all the good tweeks.
legend, reduce your sig size to forum specs. 2. An image-only signature should be less than 50kb in size, and be at most 500 pixels wide and 200 pixels tall. 4. If you want to use both text and image in your signature the image should not be more than 500 pixels wide and 100 pixels tall, and you can use up to three lines of text.