Adding customer attributes to Magento Adminhtml Order Grid.

Grid.php

 protected function _prepareCollection()
    {
        $collection = Mage::getResourceModel($this->_getCollectionClass());
		$collection->getSelect()->joinLeft(array('sfoa'=>'sales_flat_order_address'),'sfoa.entity_id=main_table.entity_id',array('sfoa.postcode'));
        $this->setCollection($collection);
        return parent::_prepareCollection();
    }

    protected function _prepareColumns()
    {

	    $this->addColumn('postcode', array(
			'header' => 'Customer Zip',
			'width' => '80px',
			'type' => 'text',
			'index' => 'postcode',
			'filter_index' => 'sfoa.postcode'));

        $this->addColumn('real_order_id', array(
            'header'=> Mage::helper('sales')->__('Order #'),
            'width' => '80px',
            'type'  => 'text',
            'index' => 'increment_id',
        ));