You can do hide and show a "Default text" in a form text field, like for example in a username login text field, we would like to show a default "username" text on it that will be cleared when user click on that text field.

That is pretty easy to do it using jQuery :

  if ($('youTarget').length != 0) {
    defaultText($('#edit-fullname'), 'Your Name');
    defaultText($('#edit-name'), 'Account Url');
    defaultText($('#edit-mail'), 'Email Address');
    defaultText($('#edit-conf_mail'), 'Confirm Email Address');
  }
  
  function defaultText(target, Message) {
    target.blur(function() {
      if ($(this).val() == '') {
        $(this).val(Message).removeClass('active');
      } 
    });
    
    target.focus(function() {
      if ($(this).val() == Message) {
        $(this).val('').addClass('active');
      }
    });
    
    target.blur();
  }

You need to understand jQuery in order to correctly invoking the function above. Cheers