Well, the best image editing program in the market is no doubt, Photoshop. The desktop pic you were mentioning is called a radial gradient. You can do it in most imaging programs but I'll need to know which program you're using to be able to guide you through. You can also adjust the image sizes in the program and sharpen it after that so that you can minimise quality loss. Why don't you join this post http://www.esato.com/board/viewtopic.php?topic=8933&forum=29 for more information and help.
