Hi Nagendra,
Add this to the global scope in config.xml. Then simply set the attribute in the quote - it gets automagically transferred to the order in the quote to order conversion process.
<global>
...
<fieldsets>
<sales_convert_quote>
<your_special_attribute>
<to_order>*</to_order>
</your_special_attribute>
</sales_convert_quote>
</fieldsets>
...
</global>
You can retrieve/set the attribute at any time via the magic getter/setter e.g.
$quote->getYourSpecialAttribute()
$order->getYourSpecialAttribute()
$quote->setYourSpecialAttribute()