If your using the latest versions of Microsoft
Internet Explorer/Netscape, just right mouse click on the picture
below and choose 'Set as Wallpaper', it's as easy as that. With
other browsers you'll have to right click and save the picture,
convert it into a '.bmp' (bitmap) format using a paint program
like PaintShop Pro and save it in the windows main folder. Using
control panel, display settings, select it under 'background',
'wallpaper'. MSIE users can do this as well for a more permanent
background.
I suggest you clickon the strech option to make
it fit the window.