[Dan203]

This may not be exactly what you're looking for but try pasting this into the head of your document...

<script language="javascript">
<!--
if (document.cookie.indexOf("bbuserid") == -1){
  if (confirm("You do not appear to be registered.\nWould you like to register now\?")){
    window.location.replace("register.php?s=&action=signup");
  }
}
//-->
</script>

Dan