Don't try and replace tables with DIV's. They are two totally different elements. A DIV is a divisional element, designed to hold and group other elements together inside. They can have set shapes, margins and a huge range of positioning properties. You need to head over to
W3 Schools and read up on how elements should be styled using CSS.
You'll find that tables are designed for
tabular content, e.g. football league scores etc, not for the layout.
Its a bit foreign at first if you're a table veteran, but you'll soon find how much better and flexible CSS based layouts are compared to tabled layouts.
CSS Zen Garden is a fantastic example of how powerful CSS is. The site has a base HTML file, however you can select different styles, submitted by the readers. The HTML doesn't change, nor the content. Just the stylesheet.