So you mean, rather than have an <img> within <div> tags, you say it's better to define the background url from within the CSS definition?
I tend to contruct a large amount of the page graphics as a single image with elements like text and buttons layered ontop. I'm trying to break out of this as it can be quite inflexible when dealing with various window sizes. I found myself using tables again (boo!).
I'll give it a go and see what happens.