NOT use it Eyefinity mode... and I do not believe I've seen a regular setup that displays different wallpaper on each monitor. I am sure it is out there, just not seen it myself.
Eyefinity = 1 big monitor, 1 image across all monitors
Windows multi monitor (extend these displays) 2 monitors, 1 image, same in each display
I did find this: http://dualmonitortool.sourceforge.net/
...and this: http://www.displayfusion.com/