Sometimes the picture you want as wallpaper isn't the right shape. It is possible to get it to fill the screen, although you will probably lose some of the photo.
(http://i40.tinypic.com/30rnrfa.jpg)
There are several picture options when setting a desktop background
If the image used for the Desktop wallpaper in Windows is not the same shape as your screen it can lead to some odd stretching of the image.
In Windows XP, right-click on the Desktop and click on Properties. Click on the Desktop tab. Click on the Position dropdown menu and select Center. You may lose some of the photo or have bars at the top and bottom or sides but the photo will not be distorted.
In Windows 7, right-click on the Desktop and left-click on Personalize. Click on the Desktop Background link at the bottom of the window that appears. Scroll down to the bottom and click on the Picture Position menu. Select Fill or Fit and click on Save changes.