You can turn on nvidia"nView" to open two desktops mode.I enjoyed it before.
The most amazing thing is that you can drag any window from one screen to the other.cool
If your asking to display seperate wallpaper for a multi-display system, you can get Ultramon, like many others said, I recommend it myself, although it is not free.
Alternately, you can do different backround in standard windows with a image editor. Simply put the two images side-by-side, make the image the size of your desktop in the editor. Make the image file "tile". Since the image is the size of the desktop you wont see the repeating of tile.