Set as Wallpaper
Click on the Options Menu and point at Set as Wallpaper. A sub-menu appears with the choices Centered, Tiled, Stretched and Previous wallpaper. Choose one to have the current image made into a background for your Windows desktop.
Centered appears as just one image on the center of the screen.
Tiled appears as multiple images, taking up the whole screen. (The desktop icons are on top of the wallpaper.)
Stretched appears as just one image on the center of the screen, but the image is enlarged to cover whole screen (non proportional).
Stretched – proportional appears as just one image on the center of the screen, but the image is enlarged using aspect ratio.
Previous wallpaper restores the image that was replaced by this operation.
IrfanView will save a BMP file called IrfanView_Wallpaper.bmp in your user settings folder (Documents and settings\User\Application data\IrfanView\) and set it as wallpaper.