From time to time I've seen people complain about how boring and unflexible HTML forms are in terms of looks. Some of the designers I've talked to really hate the default button elements, especially when it comes to the radio and checkbox elements.
I've only tested the code in Firefox and IE at the moment, but it seems to work pretty well. In order to see the full effect, your browser will have to support the insertBefore() method. Essentially what the code does is parses through the field elements in a form looking for the type of element you're skinning (currently only checkboxes and radio elements are support.) It'll then hide the element by setting the display property to "none". It'll then insert an image into the DOM right before the input element which has event's attached to the onclick event which will replicate the input element's functionality.