function positionit()
{
	var mydiv = document.getElementById("mydiv");
  mydiv.style.border = '1px solid';
  mydiv.style.zIndex = 1;
  var i = parseInt( document.body.clientWidth /2) - 364;
  mydiv.style.left = (i ? i : '0') + 'px';
	setInterval("repositionit()", 100)
}

function repositionit()
{
  var mydiv = document.getElementById("mydiv");
  var i = parseInt( document.body.clientWidth /2) - 364;
  mydiv.style.left = (i ? i : '0') + 'px';
	mydiv.style.top = document.body.scrollTop + 'px';

}