I'm not sure exactly how to do what you ask, but if you're talking about resizing ordinary images while retaining their sharpness, I believe it is impossible.
The only kind of graphics I know that you can resize without compromising image quality are vector graphics, if that's any help. They define an image's properties through mathematical calculations and ratios (so I believe), so you can make your image as large or as small as you want.
Hope that's of *some* use to you, but if there's another way of enhancing ordinary images, I'd love to hear it myself.
"Gandolf Foogray, that was my name." - <i> Gandalf, LotR (Asian Bootleg Subtitles)</i>