var elt = $('ID_DIV_TO_CENTER');
// retrieve required dimensions
var eltDims = elt.getDimensions();
var browserDims = document.body.getDimensions();
// calculate the center of the page using the browser and element dimensions
var y = (browserDims.height - eltDims.height) / 2;
var x = (browserDims.width - eltDims.width) / 2;
// set the style of the element so it is centered
var styles = { position : 'absolute',
top : y + 'px',
left : x + 'px' };
elt.setStyle(styles);
elt.scrollTo();