function openpopup(id){ 
      //Calculate Page width and height 
      var pageWidth = window.innerWidth; 
      var pageHeight = window.innerHeight; 
      if (typeof pageWidth != "number"){ 
      if (document.compatMode == "CSS1Compat"){ 
            pageWidth = document.documentElement.clientWidth; 
            pageHeight = document.documentElement.clientHeight; 
      } else { 
            pageWidth = document.body.clientWidth; 
            pageHeight = document.body.clientHeight; 
      } 
      }  
      //Make the background div tag visible... 
      var divbg = document.getElementById('bg'); 
      divbg.style.visibility = "visible"; 
        
      var divobj = document.getElementById(id); 
      divobj.style.visibility = "visible"; 
      if (navigator.appName=="Microsoft Internet Explorer") 
      computedStyle = divobj.currentStyle; 
      else computedStyle = document.defaultView.getComputedStyle(divobj, null); 
      //Get Div width and height from StyleSheet 
      var divWidth = computedStyle.width.replace('px', ''); 
      var divHeight = computedStyle.height.replace('px', ''); 
      var divLeft = (pageWidth - divWidth) / 2; 
      var divTop = (pageHeight - divHeight) / 2; 
      //Set Left and top coordinates for the div tag 
      divobj.style.left = divLeft + "px"; 
      divobj.style.top = divTop + "px"; 
      //Put a Close button for closing the popped up Div tag 
      if(divobj.innerHTML.indexOf("closepopup('" + id +"')") < 0 ) 
      divobj.innerHTML = "<a href=\"#\" onclick=\"closepopup('" + id +"')\"><span class=\"close_button\">X</span></a>" + divobj.innerHTML; 
} 
function closepopup(id){ 
      var divbg = document.getElementById('bg'); 
      divbg.style.visibility = "hidden"; 
      var divobj = document.getElementById(id); 
      divobj.style.visibility = "hidden"; 
}