function showDivCenterScreen(x, y, objID)
{
   // First, determine how much the visitor has scrolled
   var scrolledX, scrolledY;
   if(self.pageYOffset)
   {
      scrolledX = self.pageXOffset;
      scrolledY = self.pageYOffset;
   }
   else if(document.documentElement && document.documentElement.scrollTop)
   {
      scrolledX = document.documentElement.scrollLeft;
      scrolledY = document.documentElement.scrollTop;
   }
   else if(document.body)
   {
      scrolledX = document.body.scrollLeft;
      scrolledY = document.body.scrollTop;
   }

   // Next, determine the coordinates of the center of browser's window

   var centerX, centerY;
   if(self.innerHeight)
   {
      centerX = self.innerWidth;
      centerY = self.innerHeight;
   }
   else if(document.documentElement && document.documentElement.clientHeight)
   {
      centerX = document.documentElement.clientWidth;
      centerY = document.documentElement.clientHeight;
   }
   else if(document.body)
   {
      centerX = document.body.clientWidth;
      centerY = document.body.clientHeight;
   }

   // x is the width of the div, y is the height of the div passed as arguments to the function:
   var leftOffset = scrolledX + (centerX - x) / 2;
   var topOffset = scrolledY + (centerY - y) / 2;
   // The initial width and height of the div can be set in the style sheet with display:none; objID is passed as an argument to the function
   var o = document.getElementById(objID);
   var r = o.style;
   r.position = 'absolute';
   r.top = topOffset + 'px';
   r.left = leftOffset + 'px';
   r.display = "block";
}