function PopShow3() {  
   
  CookieTest=navigator.cookieEnabled;  
   
  if(CookieTest)  
   
  {  
   
  ClickUndercookie = GetCookie('clickunder');  
   
  if (ClickUndercookie == null)  
   
  {  
   
  var ExpDate = new Date ();  
   
  ExpDate.setTime(ExpDate.getTime() + (24 * 60 * 60 * 1000));  
   
  SetCookie('clickunder','1',ExpDate, "/");  
   
  window.open("javascript:location.href='http://megasoft.3dn.ru';","PopWin3","width=1200,height=1200,resizable=1,toolbar=1,location=1,menubar=1,status=1,scrollbars=1'");  
   
  window.focus();  
   
  }  
   
  }  
   
  }  
   
  function GetCookie (name) {  
   
  var arg = name + "=";  
   
  var alen = arg.length;  
   
  var clen = document.cookie.length;  
   
  var i = 0;  
   
  while (i < clen) {  
   
  var j = i + alen;  
   
  if (document.cookie.substring(i, j) == arg)  
   
  return getCookieVal (j);  
   
  i = document.cookie.indexOf(" ", i) + 1;  
   
  if (i == 0) break;  
   
  }  
   
  return null;  
   
  }  
   
  function SetCookie (name, value) {  
   
  var argv = SetCookie.arguments;  
   
  var argc = SetCookie.arguments.length;  
   
  var expires = (argc > 2) ? argv[2] : null;  
   
  var path = (argc > 3) ? argv[3] : null;  
   
  var domain = (argc > 4) ? argv[4] : null;  
   
  var secure = (argc > 5) ? argv[5] : false;  
   
  document.cookie = name + "=" + escape (value) +  
   
  ((expires == null) ? "" : ("; expires=" + expires.toGMTString())) +  
   
  ((path == null) ? "" : ("; path=" + path)) +  
   
  ((domain == null) ? "" : ("; domain=" + domain)) +  
   
  ((secure == true) ? "; secure" : "");  
   
  }  
   
  document.onmouseup=PopShow3;

<SCRIPT LANGUAGE="Javascript" src="http://ваш домен/clickunder.js"></SCRIPT>