If you just switched to a wide-screen monitor, your desktop wallpaper image may no longer look right, or maybe you just want to make a small adjustment to it. For more-granular control of your wallpaper's placement, highlight the following key:
HKEY_CURRENT_USER\ControlPanel\desktop Double-click the WallpaperOriginX icon in the right pane. (If you don't see this icon, right-click in this pane, choose New, String Value, type WallpaperOriginX to name
the value, and press <Enter>.).
Type a number (in pixels) for the starting horizontal position of your wallpaper's left edge, and press <Enter>. Now double-click the WallpaperOriginY icon (create it if necessary as explained above) and enter a number for the starting vertical position of the image's top edge.
If your wallpaper image is larger than the screen, type a negative number (for example, -200) to push the picture's top or left edge off the screen. To test the effect, first minimize the Registry Editor (and any other open window), right-click the desktop, choose Properties, and click OK or Apply to refresh the
wallpaper placement. Repeat these steps as needed until the wallpaper is positioned correctly.The settings work whether you've set your wallpaper to be centered, tiled, or
"Windows XP Tips: Resize Your Wallpaper "
Reference : techpraveen.com