Tables are just pre-laid out grids you are confined to. divs are not. You don't have to use the borders that come with CSS. You can create your own with an image editor like Photoshop and use it as a background image or place them along the edges.
I do use photoshop, but to make table backgrounds. I thought CSS only allowed you to change the top, bottom, left and right border? If this is true, then you can't really do customised corners? Or can you?