Stuart Collville and Ed Eliot’s CSS Sprite Generator tool, is the first of many in a series of web-site performance tools. CSS sprites are a way to reduce the number of HTTP requests made for image resources referenced by your site. Images are combined into one larger image at defined X and Y coorindates. Having assigned this generated image to relevant page elements the background-position CSS property can then be used to shift the visible area to the required component image.
More Info: CSS Sprite Generator