Add Category Thumbnail Images to Magento Menu

Instead of boring text dropdown menus in Magento, I want to replace some of them with small thumbnail images (preferably the thumbnail image you can add in the backend category section). This should integrate with Magento so when I add a new category and attach a thumbnail, it will automatically show up (I do not want a custom static block menu created). If possible, I would like to add some sort of a mouse-over effect so the user is aware of which thumbnail they are about to select. If you go to [login to view URL] and mouseover SHOP BY INTEREST, then mouseover a submenu, you will see exactly what I'm requesting.