function popup(url) {
    var w = 900;
    var h = 700;
    var left = (screen.width) ? (screen.width-w)/2 : 0;
    var top = (screen.height) ? (screen.height-h)/2 : 0;
    var settings = 
	'height='+h+',width='+w+',top='+top+',left='+left+',scrollbars='+scroll+',resizable';
    var win = window.open(url,'popup',settings);
}