var popupWindow;

function openPopup( url, sizeX, sizeY) {
    LeftPosition = (screen.width) ? (screen.width-sizeX)/2 : 0;
    TopPosition = (screen.height) ? (screen.height-sizeY)/2 : 0;
        if ( popupWindow) {
                if (popupWindow.closed == true) {
                        popupWindow = window.open( url, "", "toolbar=no,location=no,directories=no,top="+TopPosition+",left="+LeftPosition+",status=no,menubar=no,scrollbars=yes,resizable=yes,copyhistory=no,width="+sizeX+",height="+sizeY);
                        if (window.focus) popupWindow.focus();
                } else {
                        popupWindow.location = url;
                        if (window.focus) popupWindow.focus();
                }
        } else {
                popupWindow = window.open( url, "", "toolbar=no,location=no,directories=no,top="+TopPosition+",left="+LeftPosition+",status=no,menubar=no,scrollbars=yes,resizable=yes,copyhistory=no,width="+sizeX+",height="+sizeY);
                if (window.focus) popupWindow.focus();
        }
}