var iswindowopen = false;
var mw;

function centerWindow(theURL,winName,wSize,hSize,bar)
{
  if (iswindowopen) {
          if (!mw.closed){
            mw.close();
           }
       }
  var xMax = screen.width, yMax = screen.height;
  var xOffset = (xMax - wSize)/2, yOffset = (yMax - hSize)/2-10;
  if (navigator.appname != 'Netscape'){
  mw = window.open(theURL,winName,'width='+wSize+',height='+hSize+',scrollbars='+bar+',resizable=no,top='+yOffset+',left='+xOffset+'');
  }else{
  mw = window.open(theURL,winName,'screenX='+wSize+',screenY='+hSize+',scrollbars='+bar+',resizable=no,top='+yOffset+',left='+xOffset+'');
  }
  mw.focus();
  iswindowopen = true;
}