[Saved from a now defunct website: http://home.columbus.rr.com/luna/multimon.html ]
Written by Bret:
Check "View my Active Desktop as a web page" under Display Properties/Web.
Make a bitmap (or JPEG, but a bitmap is more desirable) that is the full size of your entire desktop.
Create a new text document in your "C:\Windows\Web\Wallpaper\" directory that contains the line:
and rename that file "Desktop.html" (replace "D:\DESKWIDE.BMP" with the name of your wallpaper).
Then you just have to go to Display Properties and select "Desktop" as your background.
If you later add things to your Active Desktop HTML, the HTML will be justified with respect to the primary display, but the background is always shown accross your entire extended desktop.
There are two good ways to organize your wide wallpapers. You can use the above method, and simply copy whatever wallpaper you want on top of "D:\DESKWIDE.BMP" (or whatever you called it), but if you like to keep several different wallpapers easily available, you can make several copies of Desktop.html with different names, and have each of them point to a different bitmap in your "C:\Windows\Web\Wallpaper\" directory. Then you can select different wallpapers from Display Properties just as easily as if they were bitmaps you had dumped in your Windows directory.