PopUp para que salga una vez

[CORE]

Código:

  <SCRIPT LANGUAGE="JavaScript">
  <!--
  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 "here";
  i=document.cookie.indexOf(" ",i)+1;
  if (i==0) break;
  }
  return null;
  }
  var visit=GetCookie("COOKIE1");
  if (visit==null){
  var expire=new Date();
  window.name = "thiswin";
  newwin=open("popup.htm", "dispwin", "width=350,height=350,scrollbars=yes,menubar=no");
  expire=new Date(expire.getTime()[phone]);
  document.cookie="COOKIE1=here; expires="+expire;
  }
  // -->
  </SCRIPT>

<p align="center"><embed src="http://usuarios.lycos.es/tlalneweb/sm.swf " quality=high width="400" height="60">