var isIE = false, isN4 = false, isN6 = false; 

var popupwin = null;
var first = true ;
var previous_url ;


function openIt(url) 
{ 
  if(document.all) isIE = true; 
  else if (document.layers) isN4 = true; 
  else if (document.getElementById) isN6 = true; 
  popIt(url); 
} 


function popIt(url) 
{ 
  var pop = new Object(); pop.w = 200, pop.h = 200;
  if (isN4 || isN6) 
  { 
    pop.top = (window.outerHeight - pop.h)/2; 
    pop.left = (window.outerWidth - pop.w)/2; pop.top += window.screenY; pop.left += window.screenX; 
  } 
  if (isIE) 
  { 
    pop.top =(document.body.offsetHeight - pop.h)/2; 
    pop.left = (document.body.offsetWidth - pop.w)/2;
    pop.top += window.screenTop; 
    pop.left += window.screenLeft; 
  } 
  features = "height=" + pop.h +",width=" + pop.w+ ",top=" + pop.top + ",left=" + pop.left+ ",screenY=" + pop.top + ",screenX=" + pop.left+",scrollbars=yes,resizable=no"; 

  if (first)
  {
     popupwin = window.open(url, "", features);
     popupwin.focus();
     first = false ;
  } else {
     if ( popupwin != null && !popupwin.closed && previous_url == url ) { popupwin.focus(); }
     else {
             if (popupwin.closed) {
                     popupwin = window.open(url, "", features);
                     popupwin.focus();
             } else {
                     popupwin.location = url;
                     popupwin.focus();
             }
     }
  }
previous_url = url ;
}