I\'m trying to add a custom field to my orders. At this moment, I found the post bellow that helped me to create such attribute in my database: http://fabrizioballiano.net/2
Add this to the gobal 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.
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You can retrieve/set the attribute at any time via the magic getter/setter e.g.
$quote->getYourSpecialAttribute()
$order->getYourSpecialAttribute()
$quote->setYourSpecialAttribute()