function PopupScreen(url,name,width,height) {
     var titleBarHeight, windowBorderWidth;
     titleBarHeight = 12;
     windowBorderWidth = 4;
 
     var screenWidth, screenHeight;
     screenWidth = 800;
     screenHeight = 600;
     if (window.screen) {
      if (window.screen.availWidth) {
       // ok browser has the appropriate properties we need to centre it
       screenWidth = window.screen.availWidth;
       screenHeight = window.screen.availHeight;
      }
     }
    
     var windowWidth = windowBorderWidth + width + windowBorderWidth
     var windowHeight = titleBarHeight + height + windowBorderWidth
    
     var left = (screenWidth - windowWidth) / 2
     var top = (screenHeight - windowHeight) / 2
     window.open(url,name,'left='+left+',top='+top+',screenX='+left+',screenY='+top+',width='+width+',height='+height+',scrollbars=0,resizable=0,toolbar=0,location=0,directories=0,status=1,menubar=0,copyhistory=0');
    }