From the site:
Single sprite (What's that?) navigation is great, but we all know it can get a little bit tedious. All that measuring of pixel perfect photoshop slices, careful coding of your CSS and subsequent calculator bashing is enough to drive anyone to start microwaving fluffy kittens. Wouldn't it be great to have a fancy online tool to take care of all the boring stuff for you in a few simple clicks?

http://labs.engageinteractive.co.uk/nav-o-matic/