var win = null;
function open_window(url,x,y){
if(win && win.open && !win.closed)
        win.close();
param = 'toolbar=0,location=0,directories=0,status=0,menubar=0,scrollbars=1,resizable=1,width='+x+',height='+y
win = window.open(url,'window',param)
};