Here is the general rule when working with floated elements. In the div wrapper that contains any floated elements, make sure to add "overflow: hidden" in the wrapper css.
For example, if you have a structure like this:
<div id="wrapper">
<div style="float: left;">...</div>
<div style="float: right;">...</div>
</div>
you would add "overflow: hidden" to the #wrapper css.
#wrapper {
overflow: hidden;
}
-justin