Soon I will post the answer:
I refer the following three links and Solved my issue hope it will be useful for others.
Ref Link 1 http://jamestombs.co.uk/2008-04-24/zend-adddisplaygroup-setting-the-legend/767
Ref Link 2: http://jamestombs.co.uk/2008-04-24/zend-adddisplaygroup-setting-the-legend/767
Ref Like 3: http://zendguru.wordpress.com/2008/11/11/applying-decorators-to-all-elements-of-form-elements-at-once/
This three links are very use full to understand the for decorative.
Answer:1
$this->addDisplayGroup(array('input1','input2','input3','input4'),
'Date', array('order' => 4,
'decorators' => array('FormElements',
array('HtmlTag', 'Fieldset'
array('tag' => 'div',
'class' => 'block',
),
),
),
)
);