You want to spread a wallpaper across two monitors?  The first thing you will need is a large enough photo… as wide as the two monitors put together, and as high as the taller of the two.  Next, in Windows 7, right click the desktop and select Personalize.  Near the bottom of that windows, click the Desktop Background link.  In that window, you can select the folder containing your desired background and the photo (or photos) you want to use.  Then, at the bottom of the window, click the Picture Position drop-down menu and select Tile – the only option that will display the image in its original size.