Ok, I played around with nView a little and found it.
Open nView in classic mode.
expand desktop management in the side menu.
Click on desktop.
click properties.
check the box for "allow different backgrounds per display".
Then select an image for each monitor.
Looks like the only main feature ultramon has over nview is the ability to have different screen savers. However, ultramon does expand the taskbar across to the second monitor, along with a few other small features. The main reason I use it is because the 7900gt does not natively support dual displays, so I use ultramon as a sort of hack.
edit: someone beat me to it, took a while for me to figure it out and write that up.
