<script language="JavaScript" type="text/JavaScript">
  <!--
  function CheckForm(e) 
  { 
  if( e.username.value=="" ){ 
  alert('Sorry, your must give us a name.'); 
  e.username.focus(); 
  return false; 
  } 
  e.username.value += ""; 
  return true;
  }
  -->
</script>
<form action="" method="post" id="myform" name="myform" onSubmit="return CheckForm(this)">
<input name="username" type="text">
<input name="B1" type="submit" value="submit"> 
 
</form>