I found this little tutorial for having different wallpapers on dual monitors without having to have special software (like Ultramon).

Dual Monitor Wallpapers without any Software
How To Use 2 different Wallpapers with Dual Monitors

Ok this Guide will show you how to use Multiple Wallpapers On Dual Monitors. I will be showing you without any additional Software needed.

Step One: Right click your desktop, then select Properties.

Step Two: Locate the Desktop Tab and click On it.

Step Three: At The bottom of the Desktop Tab Select the Customize Desktop Button.

Step Four: Now in the Desktop Items window that just popped up go to the Web Tab.

Step Five: Click the New Button on the right of the window and select your second wallpapers location.

Step Six: select ok, then select Ok again on the Web Window and Apply on the Desktop Window. now your pic should be on your main screen.

Step Seven: Now click image and when bar appears at top, drag the Image over to the other Screen, and select Cover Desktop at the top left of the image.

Right click and select Arrange By and "Lock web items on desktop." Now you can select a standard desktop for your primary display and use the web object to cover the standard desktop image on your second desktop with the image of your choice."

Mine looks like this, 22"on left and 19" on right.



Hope this is useful to someone.