function centerPopUp(centerPage) {
  var myWidth = 0, myHeight = 0;
  if( typeof( window.innerWidth ) == 'number' ) {
    //Non-IE
    myWidth = window.innerWidth;
    myHeight = window.innerHeight;
  } else if( document.documentElement &&
      ( document.documentElement.clientWidth || document.documentElement.clientHeight  ) ) {
    //IE 6+ in 'standards compliant mode'
    myWidth = document.documentElement.clientWidth;
    myHeight = document.documentElement.clientHeight;
  } else if( document.body && ( document.body.clientWidth ||  document.body.clientHeight ) ) {
    //IE 4 compatible
    myWidth = document.body.clientWidth;
    myHeight = document.body.clientHeight;
  }
  w = (myWidth/2)-175
 document.getElementById(centerPage).style.left = w + 'px';
 document.getElementById(centerPage).style.top = '180px';

}

function showPopUp(whichPage) {
 centerPopUp(whichPage);
 document.getElementById(whichPage).style.visibility = 'visible';
}

function hidePopUp(whichPage) {
 document.getElementById(whichPage).style.visibility = 'hidden';
}