enlarging an image while keeping its quality

hi,
I am looking for a software (or a way) to enlarge an image while keeping its quality or sharpness. I tried Kenson Imagener. But when I increased the image size the image just got blurry. probably I am not entering the right setting i have a 640X470 sized image and I want to increase it to 1024×768 to make it a desktop wallpaper.
I wanted to try Bearded Frog Enlarger Pro. But can’t find a valid link.
Any suggestions.
Answer #1
Frog Enlarger Pro
http://~ Dead file host ~/files/9444516/P-FE302.rar