The easiest way without JavaScript to center a DIV tag is to use a style tag or css that resembles the following.
style=’padding:5px;width: 400px;height:200px; margin-top:-100px; margin-left:-200px; left:50%;top:50%; border:outset 1px #ccff99; background-color:#ccff99;position:absolute;font-weight:normal;’
Sample Image