As it is, you should be able to change each monitor's background separately if you have the display in "Extended" mode. If it's in clone, or in stretched (which single, dual-head ATi cards dont support you cannot, but the default windows mode will allow you to do so.
nothin's workin so far -_-' how do u install ultramon? It unzipped to desktop, but I couldn't find any directions on what to do next? i'll check the site one more time to make sure...