<script language="JavaScript">
 <!-- 
function checkform()
  {	
   if (document.f.Name.value == "")
   {
   alert("Sie haben vergessen, Ihren Namen einzugeben.");
   document.f.Name.focus();
   return(false);
   }
   else return(true);         
  }

</script>
<form method="post" name="f" action="baseportal.pl?htx=/Anmeldung" enctype="multipart/form-data" submit="return checkform()">