protected function _prepareToRender()
    {
        $this->addColumn(
            'installment_currency', array(
                'label' => Mage::helper('adyen')->__('Currency'),
                'style' => 'width:100px',
            )
        );
        $this->addColumn(
            'installment_boundary', array(
                'label' => Mage::helper('adyen')->__('Amount (incl.)'),
                'style' => 'width:100px',
            )
        );
        $this->addColumn(
            'installment_frequency', array(
                'label' => Mage::helper('adyen')->__('Maximum Number of Installments'),
                'style' => 'width:100px',
            )
        );
        $this->addColumn(
            'installment_interest', array(
                'label' => Mage::helper('adyen')->__('Interest Rate (%)'),
                'style' => 'width:100px',
            )
        );
        $this->_addAfter = false;
        $this->_addButtonLabel = Mage::helper('adyen')->__('Add Installment Boundary');
    }