function open_window(url, name, width, height) 
{ 
     var top, left, features; 
      
     top = (screen.height / 2) - (height / 2); 
     left = (screen.width / 2) - (width / 2); 
           
     if(top < 0) 
          top = 0; 
           
     if(left < 0) 
          left = 0; 
 
     features = 'scrollbars=1,location=0,menubar=1,status=0,width='+width+',height='+height+',left='+left+',top='+top+',resizable=1'; 
      
     window.open(url, name, features); 
}