Ah - good choice - this is one of my favourites! I suppose you what to know how to get it on the desktop now. You can set the wallpaper as you desktop in a number of different ways. You can either right click the background below and then choose 'save target as...' (IE & Opera) or 'save link as...' (Firefox). If you do this - remember where you saved it! Next goto where you set the desktop background for your particular computers operating system and select the image from the location where you saved it.
A different way altogether is to right click the background below, from here choose 'save image as...' or 'set as Desktop Background' or 'Set as Background'. You'll know what to do when the time comes. I think you have it in you. My guess is you already know. I'll keep a lid on it now.
Return to wallpaper thumbnails.